New build for the 6.5 Grendel Wildcat fans... 6mm Fat Rat

[Lofty]

Im keeping a tab on this to see how this progresses.

Im gonna call Lee tomorrow to discuss some options.


The only real downside is the lack of brass options. I will be shooting this in tactical matches and you can always expect to lose 30-40% of your brass. That Lapua brass aint cheap.

 

[Fried Chicken Blowout]

Im keeping a tab on this to see how this progresses.

Im gonna call Lee tomorrow to discuss some options.


The only real downside is the lack of brass options. I will be shooting this in tactical matches and you can always expect to lose 30-40% of your brass. That Lapua brass aint cheap.

I'm torn what what to do with the brass issue. It's a lot of money considering I'm using all Lapua and even the Hornady is not much less. I think I would use a brash catcher during any run and gun type stages. Some matches will also allow you to use a different upper if you carry it with you all the time. Not sure if it would be worth it to carry an SBR upper in the pack just to shoot .223 and leave the brass on the run and gun stuff or not. But figuring each piece of brass that's lost you figure you have the cost of the brass it self as well as the compoents and time used during the fire forming tied up in it so that's at least $1.50 per piece.

 

[Lofty]

Yeah, a brass catcher might be the only thing that makes this caliber feasible as a tactical match rifle.....or winning the lottery.

Ive heard of malfunction problems though with a brass catcher, something about it bouncing shells back into the chamber when the bolts open.



I like that handguard.........what did that run you if you dont mind my asking.

 

[Fried Chicken Blowout]

Went out to Colorado Rifle Club today and shot the 105gr Nosler Fire Forming loads out to 550 yards. All ran smooth and super consistent, it's all very impressive. The calculated velocity based on the 550 yard validation is 2820 fps. Here's a trajectory sheet done up out to 1000 yards based on the 550 yard validation, of course actual trajectory beyond the validated distance is subject to change based on reality when I get a chance to go out farther.




Import 4 by FriedChickenBlowout, on Flickr

 

[Fried Chicken Blowout]

I like that handguard.........what did that run you if you dont mind my asking.

The hand guard is super badass... I love it. It's made by Carbon Arms right here in Colorado by a couple of serious shooters. They sell them on their own website, but Brownell's has them too.

Carbon Arms Feather Handguard


It's $186 at Brownells with the dealer/mil discount.

AR-15/308AR Carbon Feather Handguards | Brownells


I used a JP rail segment for the bipod mount and Impact Weapon Components sling stud mounts. Just drills the holes where you want them and mount up your accessories.

 

[Lofty]

Thanks for the heads up on that. Gonna pick one up. I have an 18 inch DMR styled rifle that I plan on cannibalizing for this project. Its got a 13 inch rail on it but that isnt long enough with the gas tube length it looks like.

Also, I saw you had some mag issues. Sorry if I didnt understand. Do you have to use Grendel mags, or can you use Magpul 20 rounders?

 

[Lofty]

BTW....if the rest of that chart tracks true....7.7 mils out to 1000 out of an AR15 based gasser is just phenomenal.

 

[Fried Chicken Blowout]

BTW....if the rest of that chart tracks true....7.7 mils out to 1000 out of an AR15 based gasser is just phenomenal.

And that's just with the Nosler bullets. I ran the numbers with the 105gr Berger Hybrids and it looks like 7.4 mils at 1000 if theory equals reality... I'll start doing some load workups on the Bergers this week and next.

 

[Fried Chicken Blowout]

Also, I saw you had some mag issues. Sorry if I didnt understand. Do you have to use Grendel mags, or can you use Magpul 20 rounders?

They are Grendel mags, the internal ribs are smaller making the mag wider inside and they are longer. You can load out just past 2.29 in these mags. The follower is different as well as the feed lips being shorter.

 

[Scotts556]

Well got me sold on it. Can you choose what upper he uses?

Scott

 

[Fried Chicken Blowout]

Well got me sold on it. Can you choose what upper he uses?

Scott

He has the standard Mil-Spec ones in stock. The fit and finish on the ones he's using is outstanding. I was initially concerned and wanted a VLTOR but didn't have one on hand to send him. You can order a barrel and bolt and build it yourself or contact him about supplying the upper that you want.

 

[Scotts556]

He has the standard Mil-Spec ones in stock. The fit and finish on the ones he's using is outstanding. I was initially concerned and wanted a VLTOR but didn't have one on hand to send him. You can order a barrel and bolt and build it yourself or contact him about supplying the upper that you want.

Thanks

Scott

 

[Lofty]

Where are you picking up brass? Grendel brass seems to be notoriously hard to locate.

 

[Unknown]

Places I have bought 6.5 Grendel brass:

Alexander Arms
Powder Valley
Russ Haydon's Shooter's Supply
Bruno Shooter's Supply
Midway
E. Arthur Brown
Graf and Son's

You will need to do the same thing I do..go to each site, and see if anyone has it in stock, and how much they charge for it. I have paid from $70-98 per hundred.

Additionally, I found that the flash holes on Lapua cases are not uniform. A 1/16 inch drill bit brings the small ones to the same size as the large ones. A 1/16 bit just passes through the large flash holes, so I uniform them. I haven't tested to see if it makes any difference, but I like knowing they are all getting the same ignition start.

 

[Fried Chicken Blowout]

I've been getting the Lapua brand grass from Mile High Shooting here locally for $93 per box + tax. I checked today and they have 30+ boxes on hand now. MidwayUSA also has the AA branded Lapua brass in stock as well as the Hornady.

 

[LRRPF52]

Excellent thread. Another affordable consideration is to use 1xfired PPU Grendel or 7.62x39 brass for run-and-gun stage expendables, but that requires different load work-up because of case capacity. $93/100 is insane. AA usually has the best prices on Lapua brass (AA brass is Lapua headstamped Alex-A).

The "17rd mags" were never what they were supposed to be. A curved body mag was originally spec'd, and CProducts sent AA the straight body one, which failed miserably for reliability testing when loaded to capacity. AA never carried it as a product as a result, and only stocks/ships 4rd, 10rd, 24-26rd mags.

As far as barrel extensions coming loose, Bill A. explained to me that when you push the pressures in the AR15 barrel extension with a case that has more bolt thrust, it can and will shift the thread tenon to the point that the forward shoulder of the extension is no longer holding tension against the shoulder of the barrel. There was a guy who consistently loaded the Grendel hot, and experienced the same thing-loose barrel from the extension.

Maybe the method Bustin explains can help with that in a high-pressure case with a larger head than .378" like the .222 Rem and 5.56 NATO. The original gun was built around the .222 Remington, and never adjusted for the 5.56x45 pressures, since they figured it was good enough.

 

[gswaney]

I am interested in the velocities you get as you test with different bullets and powders. I have a 6rat (not the fatrat) and get nowhere near the advertised velocities others say they do. I am about ready to give up on this thing. Anything over 2700 fps with a 87, 95, 105 amax or 107 flattens and craters the primers. I even neck turned to get more clearance than the fatrat and no change. This brass is too expensive to trash in several outings. The fatrat has.0015 fatter case, .002 larger neck and .001 shorter lead so it may also have the same issues. I don't have the cash to spend having it opened up to a fatrat unless I get convinced it will cure the pressure problems. I heard WOA has stopped offering this chamber because of bolts breaking. I haven't verified it. The 6 hagar sure is looking like the way to go. The brass wasn't available when I bought the rat so I thought this was the hot setup..

Gary

 

[Fried Chicken Blowout]

I am interested in the velocities you get as you test with different bullets and powders. I have a 6rat (not the fatrat) and get nowhere near the advertised velocities others say they do. I am about ready to give up on this thing. Anything over 2700 fps with a 87, 95, 105 amax or 107 flattens and craters the primers. I even neck turned to get more clearance than the fatrat and no change. This brass is too expensive to trash in several outings. The fatrat has.0015 fatter case, .002 larger neck and .001 shorter lead so it may also have the same issues. I don't have the cash to spend having it opened up to a fatrat unless I get convinced it will cure the pressure problems. I heard WOA has stopped offering this chamber because of bolts breaking. I haven't verified it. The 6 hagar sure is looking like the way to go. The brass wasn't available when I bought the rat so I thought this was the hot setup..

Gary

I've had no primer pressure issues. I even loaded a couple with Federal pistol primers that were stuck in my Dillon primer loader. Those were the only ones that cratered at all because they were so soft. If my ballistic calculations are correct my 2820 is still under what it could be making. My test loads showed that I could be up at 30grs of Reloader 15 if I wanted to push it. I'm making 2820 at 29.4grs. Not sure if you used R15 but I'd be curious to hear what load you're getting the pressure signs at.

 

[gswaney]

The loads that I have tested so far has only been aprox: 150 rounds after fireforming. To this point I have not hit 2800 others say they get with anything without extreme pressure signs. Actually every load fired has had the pressure signs no matter which load. The names on the cartridge face are almost unreadable, they have ejector smears and cratered primers.

Loads tried after ff were:

26" WOA , 1-8 Kreiger barrel.

R15 29gr, AA brass, CCI450.
Sierra 95's 2755 average.
Sierra 107's .016 off, 2790 avg.

8208, 28grns, AA brass, CCI450.
S 95,s, 2.270, 2755 avg.
S 107's, .016 off, 2690 avg.
107 amax, .002 off, 2700 avg.


8208, 28.3 gr, AA brass, CCI450.
S 95's, 2.27oal, 2780 avg.
S 107's .016 off, 2800 avg.
105 amax, .002 off 2735 avg.


Tried 8208 28.5 grns before backing down to 28.3. It was a little faster for some shots but lower for others (??) but pressure issues stopped that test quickly.
Totally erratic readings for some reason. Could be the loads or chrono (oehler). Who knows. By this time I gave up on this. I am becoming interested again after 2 years in working with the rifle again and plan to start at 28 grns. R15. Some love the 8208 but I just don't like the narrow pressure band and spikes.

I hope this info was interesting and I will post more as I go. Please keep sharing your results.
gary

 

[Jon A]

I wonder if you have a headspacing issue or something. Have you tried backing off the resizing die a ways and seeing if you can still chamber the brass?

 

[Fried Chicken Blowout]

I wonder if you have a headspacing issue or something. Have you tried backing off the resizing die a ways and seeing if you can still chamber the brass?

Speaking of which... I bought a backup bolt from Lee when I ordered the upper. He didn't have two at the time he shipped mine so I was waiting on another to come in. He emailed to say that there was a change in the AA bolts and new ones would head space different by 0.003 and that was an issue. He had me measure the depth of my bolt face and I'm waiting to hear back to see if these new ones will work with my barrel. Did you change the bolt head?

I would also increase your bullet jump. Those that are 0.002 off the lands may be giving you an issue. I had this happen with my .223 long range gun where I was loading a mag length which was too long for some 75 gr bullets. What happens to your pressure signs if you increase the same load to 0.015 - 0.020 off the lands? The load I'm using now is WAY off the lands and it's still super accurate. Hopefully I don't end up with pressure issues when I switch to the Berger Hybrids which I can get all the way into the lands if I want. I'm gonna load my ladder rounds tomorrow and should know where they get pressure signs by Tuesday night.

I would call Lee and talk to him about the pressure issues and see what he would charge to ream your chamber to the Fat Rat specs. I think the money would be worth it to be able to run a hotter load.

 

[Fried Chicken Blowout]

Some love the 8208 but I just don't like the narrow pressure band and spikes.

Lee said the R15 was good but the H4895 was better for the heavy loads. I can't find any anywhere so I'm using the R15 which has been very good so far. That being said if you can find any H4895 then jump on that as well.

 

[gswaney]

Thanks guys. I have already emailed Lee. The head space should be fine. I bumped it back .004. The bolt came from Holliger with the barrel. It is a LMT that he recommended. In the mean time I am going to play with some loads and see what I get. This is a great discussion.

 

[Fried Chicken Blowout]

I have already emailed Lee.

Lee is hit and miss with emails. I can send him 4 questions and get an answer to two of them. I'd call if I were you.

 

[gswaney]

I will call in the am. I loaded some sierra 95's to just try a milder load with necked down cases to help with the tight chamber neck. I lowered the charge to 28.5 R15, 2.27 oal and Br4 primers. I didn't bother with a chrono because I just wanted to check for pressure signs after neck turning. I STILL have flattened primers. No cratering though but still bad with that weak of a load. Only held a 10 round group about 1 moa at 100 yds.
And thats off the bench with a scope. Still sucking eggs. Last resort is to rechamber to the fatrat.

gary

 

[Fried Chicken Blowout]

I STILL have flattened primers. No cratering though but still bad with that weak of a load.

gary

I've always had what I would consider flattened primers on all my AR loads in .223 or Fat Rat. I judge pressure more on the ejector marks. How noticeable are you ejector marks?

 

[gswaney]

Most of my AR loads have fairly flat primers also but with this load today I still had ejector smears same as before with all the above loads I tested.

 

[Fried Chicken Blowout]

Got some more data today. Loaded up two sets of Berger 105gr Hybrids (G1 BC 0.547) to shoot ladder tests with. First off let me apologize by correcting a prior post of mine where I stated that the Hybrids would hit the lands before they were outside of the mag length. This is not correct and I'm not sure what happened in my initial measurements with the COL gauge. These bullets actually hit the lands at a COL of 2.384 with max mag length being 2.290 - 2.300 depending on the mag. I ended up loading these to 2.290 which gives me a 0.094" jump to the lands. The loads were made on virgin Lapua 6.5 Grendel (Necked down to 6mm Fat Rat of course) brass with Reloader 15 and CCI #41 primers. I made two sets of test loads that were identical starting at 29.0gr and going to 30.0 in 0.01gr increments. My real goal was to see if where the pressure signs creeped in at so I would know where I wanted to load up some more test loads. I was also testing as a very basic ladder to see if there was any change in POI within that spread of loads. This was done only at 100 yards as this is the best controlled enviroment I have since I have access to a 100 yard indoor range.

I then placed two targets on the same backer side by side and ran it out to 100 yards. Loaded up the two identical rounds in the mag starting at 29.0gr. The first round fired would be chambered via the bolt catch into the target on the left (first target in post) and the second round would be chambered automatically fed and fired into the target on the right (second target in post). I did not rebuild my position between shots. I simply shifted my point of aim and fired so there was some tension in my position on the second target that was not there in the first which was shot all natural point of aim. A Bulls Bag was used for a front rest and a TAB gear square rear bag was used for a rear rest. My initial intention was to recall the target and mark it for each impact so I would know which ones went where but I ended up with one large group that was 1/2 MOA for 9 rounds and one flyer in each group. The first target's flyer was all me, I blinked and flinched with the trigger break. The second target's lowest shot I have no reason for, it was 29.6gr and just went low.

The target on the left really had a random set of hits within that 1/2 MOA hole. The target on the right basically tracked upward as the grains increased and went back and forth with each shot fired. It was kind of interesting to see that group shape up as it did. 29.0 on the second target was the second to the lowest shot on the target and the lowest was the oddball one but other wise they just went directly up as they powder load increased. I did not fire the 30gr load into the ladder target as the pressure signs on 29.9 were already enough I knew I didn't want to consider 30.0 so I shot those into another target.

There is almost no ejector marks on the cases until 29.5 grs and at 29.9 I would consider them to be the same as what is seen on Lake City 5.56 cases when fired. On 30.0gr you could see a shadowed imprint of ejector that smudged from the bolt unlocking. There were no cratering of primers and no pierced primers at at any powder level. There is however damage to the case head that is being done by the back side of the extractor on random cases. This does not appear to be related to the powder level. I'm wondering if this has to do with the head spacing of the fire forming cases on the 6.5mm neck portion being too tight into the chamber. Or it could of course just be an out of spec extractor that I need to deburr. Based on this I think I would be okay loading anywhere in this range but I'm likely gonna stick with 29.4gr as it keeps the cases without ejector marks. I'll play around more with the load when I'm using the fire formed cases. But accuracy seem superb at this time, even with the fire forming cases.

At the conclusion of today 128 rounds have been fired through this upper, 75 of those being fired since the last cleaning.

Constructive questions and comments are welcome. This is my first time working up a load for rifle this accurate so I'm learning as I go. If my thought process is way out of line with acceptable standards I'm happy to be educated.


Untitled by FriedChickenBlowout, on Flickr





Untitled by FriedChickenBlowout, on Flickr

 

[steve123]

Your 6mmFR is shooting so good at 100Y it looks like it'd be hard to tell where the optimum charge is at 100Y. I'd say to do a proper double ladder test at 400Y and judge by vertical dispersion. It helps to have calm conditions (early AM) and it's important to let the barrel cool. My method is a real PIA but it works well. I shoot a couple foulers to warm up the barrel and make sure I'm zeroed at 400Y, drive down and tape them. Then fire 2 rounds (lightest charge) and drive down to mark them 1 and 1, 2 and 2, repeat, repeat...I like that the barrel cools the same amount of time between shots because of the drive.

I bought one of those 3" wide aluminum sleds that attach to the bottom rail on my AR from Whidden to shoot off the benchrest. Definitely tightens my groups up.

Here's ladder I did at 330Y with 115DTACS when I first got my 6mmART. Pretty easy to tell where the node was, aye?

 

[Fried Chicken Blowout]

Sounds like I plan. I have a date with the outdoor range on 9/5 so I'll get some more loads made up and do another ladder at the longer range to see how it does. Thanks for the info.

What do you think of the 115 DTACS out of the little case. Lee advised me that the 115gr bullets were too heavy to get enough speed out of them and suggested staying with the 105-107gr bullets. Are you single loading those or mag feeding them? I'm not interested in single loading at this time so that my be a limiting factor.

 

[steve123]

Sounds like I plan. I have a date with the outdoor range on 9/5 so I'll get some more loads made up and do another ladder at the longer range to see how it does. Thanks for the info.

What do you think of the 115 DTACS out of the little case. Lee advised me that the 115gr bullets were too heavy to get enough speed out of them and suggested staying with the 105-107gr bullets. Are you single loading those or mag feeding them? I'm not interested in single loading at this time so that my be a limiting factor.

Lee is correct. At the time I curious and wanted to see for myself. 2675 fps was the fastest they would go and yes I was mag feeding them.

 

[Fried Chicken Blowout]

Ended up doing some more loads today. I loaded up two more 0.1gr ladders from 29.1 to 30grs to shoot at longer range before I load up the rest of my brass that needs to be fire formed. But I also loaded up a couple control groups to shoot over the chrono. I'm interested to see how much more speed I get out of the fire formed brass at the same charge weight. I'm assume it will be a higher velocity since there is not any energy being expended to form the brass. But I'm sure you guys that have been fire forming know the answer to this already. One other interesting thing to note is that the fire formed brass is actually shorter than the initially neck sized brass.

The length of the initial neck sized brass before reloading was 1.521.



Untitled by FriedChickenBlowout, on Flickr


Max case length calls for a length no longer than 1.525 with a trim length of 1.520. But the freshly fire formed brass is measuring 1.509 which I don't think will be an issue, but it was interesting to see. I would highly doubt my case trimmer will see any use with these cases.


Untitled by FriedChickenBlowout, on Flickr


While I was also whipping out some of my .223 match loads I decided to take a picture of the bullet I have been using for .223 next to it's big brother for the Fat Rat. The bullet on the right is the Berger .224 80.5gr Full Bore Target BTHP which is usable at AR mag length that I actually load to 2.26" COL. The bullet on the left is the Berger 6mm 105gr Hybrid.


Untitled by FriedChickenBlowout, on Flickr


And I'll leave you with a comparison photo of the progression of the 6mm Fat Rat loads ending with a loaded .223 round for scale. Starting on the left you have the virgin 6.5 Grendel Brass, then you have a loaded fire forming load that's been necked down and holds a 105gr Hybrid, then you have a formed load with the 105gr Hybrid followed by the .223 round with the 80.5gr Full Bore. I'll be hitting the outdoor range to test everything out on Thursday. I hope to have some updates that night.


Untitled by FriedChickenBlowout, on Flickr

 

[Fried Chicken Blowout]

Went to the outdoor range today to get some more load data and took the chrono this time. Because I was gonna go down range every couple of shots and wanted to drive I could only use the 200 yard range. Ended up shooting another ladder of loads between 29.1 and 30gr of Reloader 15 in 0.1gr steps. Found that there is two nodes. 29.3, 29.4, 29.5 all group in the same hole at 200 yards. 29.1, 29.2, 29.6, 29.7 are outside the group and then 29.8, 29.9, 30 start to group back together a little higher than the other group. In my prior testing 29.4 shot the best groups in the past so I'm gonna stick with that as it shows no real real pressure signs. There was intermittent mild createring of the CCI#41 primers at 29.5 and above but it didn't happen all the time.


Untitled by FriedChickenBlowout, on Flickr

Of the two ladders I shot here's the chono data for the 105gr Berger Hybrids seated to 2.290 over Reloader 15 in the Lapua 6.5 Grendel Brass.

29.1grs - 2755/2722
29.2grs - 2788/2762
29.3grs - 2793/2794
29.4grs - 2800/2794
29.5grs - 2802/2805
29.6grs - 2797/2813
29.7grs - 2822/2821
29.8grs - 2825/2835
29.9grs - 2847/2843
30.0grs - 2856/2835

As I was assuming that 29.4grs would work well I did 10 test rounds (fire forming brass) at that load and shot those over the chrono to make sure that load was consistent. Here is the result of a 10 shot string fired 10 feet from the chrono in a DA of 7308 ft.

Average = 2804 fps
Standard Deviation = 6.2 FPS
Extreme Spread = 20 FPS

Hopefully I ran the numbers correct. I used an online calculator to get the SD. These loads also showed less pressure signs than the Nolser 107gr bullets that I initially did some testing with at the same charge weight.

And out of curiosity I also loaded up 10 rounds on FORMED brass. These were my first rounds that I loaded on fire formed brass. I used the same Berger 105gr Hybrid at the same 2.290" COL and the same 29.4grs Reloader 15. Here's the results from that string of 10 rounds over the chromo.

Average = 2826 fps
Standard Deviation = 9.5 fps
Extreme Spread = 27 fps

As you can see there is a jump in SD and ES. I would assume this is due to the extra case volume and it not being filled causing some burn rate changes. But now that the brass has been formed the average speed is up 22 fps. My assumption is when I work up a load for the fire formed brass I'll either push up into the higher node or change powders to get more case fill. If anyone has any input on this please let me know if I'm on the right track.

 

[Fried Chicken Blowout]

Got the Seekins lower all built and tested. Ran into an issue the first time out. I built it the exact same as the initial lower seen in the first set of photos with the Geissele High Speed Match trigger. Well the new Geissele that I got from Brownell's didn't like the pin position in the Seekins lower. The hammer was dragging on the bolt carrier so much I had to open the gas all the way up to get it to run. Ended up swapping the fire control groups between the two lowers and all is well. The questionable hammer functioned without issue in the other lower and all was well. Seekins and Geissele were both very helpful and friendly when I called to ask where to start to track down my function issue.


Untitled by FriedChickenBlowout, on Flickr


The Seekins lower is very impressive. Kind of built like a brick shit house so to speak. The mags fit a little tighter with less rattling in the Seekins lower which is nice. I was initially hesitant sticking a forged upper on what I didn't realize until after I bought it was a billet lower. But Seekins did a nice job making the subtle details match up so it would work with a standard mil-spec forged upper as you can see in the photos of the left side where they made it match up. I've been using the Power Custom Receiver Shims in my precision ARs to totally tighten them up. This upper requires one shim with either of the lowers. My Vltor upper on my .223 also requires one with either lower. They slide right in and with the help of the tension screw in the rear, all the slop is totally gone.


Untitled by FriedChickenBlowout, on Flickr


Also went by Mile High Shooting to get a measurement with the Reaper can attached. Didn't want to screw up and get a case it wouldn't fit into. Not quite sure I'm gaining any size savings over an AR10 at this point with it being 50.5" long with the suppressor attached. Looks like I still have another 4 months on my Form 4 according to Mile High.


Untitled by FriedChickenBlowout, on Flickr

 

[steve123]

Your AR Rock's man!

I won a side charger Grizzly upper receiver once, coolest upper receiver going IMO, sold to a friend and he turned it into a 6BR.

Stop posting about awesome AR's, you're making me want that 224R now.

 

[Fried Chicken Blowout]

It was a long weekend of loading. And I'm headed back to Mile High Shooting tomorrow for 200 rounds more brass to finish off this jug of Reloader 15. After I shoot most of these I'll start work on the new load for the formed cases.



Untitled by FriedChickenBlowout, on Flickr

 

[daxromana]

Do the fire formed loads get more of a defined shoulder after one or two more firings? It looks a little rounded.

Also, awesome thread. This has been very thought provoking.

 

[Fried Chicken Blowout]

Do the fire formed loads get more of a defined shoulder after one or two more firings? It looks a little rounded.

Not totally sure... I've heard they form better with flat base bullets and I'm using BTHPs so that could be the case. I've only shot 10 rounds twice and I was too dumb to keep the brass sorted out at the range. It didn't look different enough to catch my eye when I was picking it up. The one I used in the photo above to show the progression may have been one of the lighter loads I did in the ladder and didn't form all the way. If you look up higher to the shot of the case in the caliper the shoulder seems a little more squared off. Here's a photo from Lee that shows one of his cases and it seems a little shaper.



6MM_Rat_vs_6.5_Grendal_008_op_656x648 by FriedChickenBlowout, on Flickr

 

[nmjwolf]

I've had some of my initial fire form loads not have crisp shoulders here are 3 all shot with same load where one case has the rounded corners. Follow-on shooting squares off the shoulder.

28.5g Varget CCI400 primer and 105 berger hybrids

 

[Fried Chicken Blowout]

The moment I've been waiting for....

After completing 700 rounds of new 6mm Fat Rat ammo on virgin Lapua brass with Berger 6mm 105gr Hybrid bullet on 29.4gr Reloader 15 with CCI #41 primers, I was able to hit the range today. The goal? Shoot the 6mm Fat Rat past 1000 yards. Before that I needed to zero the for the new load. The gun was zeroed for the prior Nosler load. The top left shot was the prior zero and then a quick adjustment got me the 5 round group in the center. All seemed well after cleaning the barrel the night before.



Untitled by FriedChickenBlowout, on Flickr


After that we jumped out to a shoot positions at 344 yards (1.2 Mils) and 538 yards (2.8 Mils) and plugged first round hits on 12" targets based on the chrono provided velocity 2804 fps. Just a click here and there was needed to get center hits on the target.



Untitled by FriedChickenBlowout, on Flickr


The next shoot position was at 840 yards (5.8 Mils) with the wind picking up some ranging from 5 to 15 mph from 90* right. A large 16"x24" AR500 target was used to get the first hits and dial in elevation. After that I switched back to the 12" steel and obtained 4 out of 5 hits. I ditched one of the rounds when the wind lulled. The 4 shots on target had a 3.5 - 4" vertical spread.



Untitled by FriedChickenBlowout, on Flickr


The last shoot position for the day was at 1040 yards (8.3 Mils) with the wind remaining about the same. Again the large target was used for dialing elevation and then I confirmed hits on the 12" target. This time I made 3 of the 5 rounds fired on the 12" target. This time the vertical spread was right at 3". Both rounds I missed were do to over estimating the wind. The 12" x 3/8" AR500 target mounted on rubber straps has plenty of movement when it to call hits, but the round lacks significant energy to blast off the multiple layers of paint except for directly under the point of contact with the bullet so the bullet impacts where not as easy to spot as they were in the photo above when shot from 840 yards.

Throughout the day everything was very consistent and no function issues popped up. The new brass bag that I attached to the bottom of my pack worked out great. Just fold it out and drop in fist fulls of brass and throw the pack on your back and go. The mouth stays shut on it's own and brass pickup is quick and easy. I'm planning on using this at field bases matches so I don't loose a bunch of this stupid expensive brass.



Untitled by FriedChickenBlowout, on Flickr




Untitled by FriedChickenBlowout, on Flickr



Untitled by FriedChickenBlowout, on Flickr



Untitled by FriedChickenBlowout, on Flickr


One thing I found interesting was the comparison between the 6mm Fat Rat and my buddy's 6.5 Creedmoor. He brought along his Savage 12 LRP in 6.5 Creedmoor. Shooting factory Hornady 140gr AMax loaded ammo through it's 26" barrel there was some striking similarities. Notice in the data cards below that, at almost every range, the 6mm Fat Rat and the 6.5 Creedmoor are within 0.2 Mil of each other in both drop and windage. They start out within 20 FPS at the muzzle and the 6mm Fat Rat bleeds off more speed over the 1040 yards but the drop remains pretty similar and there is a big difference between the foot pounds of energy.

6mm Fat Rat

6mm Fat Rat by FriedChickenBlowout, on Flickr


6.5 Creedmoor

6.5 Creedmoor by FriedChickenBlowout, on Flickr


Had a great time at the range today and I'll be back at it next week to actually to some specific training rather than testing and data gathering.

 

[McLarenross]

This is great! Please keep up this thread. I cannot wait to get home and be able to start building my own 6 Fat Rat or 6 AR Turbo 40. The performance this cartridge gives from a small frame gun is amazing! Thank you so much.

 

[mlc0341]

I have a 6mm rat on a AR-15 26" barrel and I love it I use it for 1000 yard target and it will do a number on white tail. I use hornady 105 amax seria match king 107 and burger hybrid 105 my fav. Is the burger 105 with 29.5g RL-15

 

[Fried Chicken Blowout]

It is the Berger 105gr Hybrid that I'm shooting with 29.4gr RL-15, my testing showed that 29.2 - 29.5 all shot to the same POI so I went with 29.4gr. The Nosler load that I worked up liked that same charge weight as well but didn't shoot as good as the Bergers. What charge weight are you using for yours? I'll start working up some loads on the formed brass here shortly and see what happens. So far ALL the load development I've done has been on virgin 6.5 Grendel brass from Lapua with just a neck size to 6mm. I also didn't do any prep to the brass. Just size the neck, clean the lube off and load it.

 

[ci11]

It is the Berger 105gr Hybrid that I'm shooting with 29.4gr RL-15, my testing showed that 29.2 - 29.5 all shot to the same POI so I went with 29.4gr. The Nosler load that I worked up liked that same charge weight as well but didn't shoot as good as the Bergers. What charge weight are you using for yours? I'll start working up some loads on the formed brass here shortly and see what happens. So far ALL the load development I've done has been on virgin 6.5 Grendel brass from Lapua with just a neck size to 6mm. I also didn't do any prep to the brass. Just size the neck, clean the lube off and load it.

Thanks for the great thread and meticulous reporting!

BTW, what's the measured water capacity of fireformed Lapua cases in your barrel? With virgin 6.5G Lapua cases, I'm right around 35.1 and 1x-fired Hornady at about 36.0.

 

[Tireguy]

FCB-

Are you shooting these 105s mag length or seating the bullet out further for single loading?

I have had the 6FatRat for almost 2 years and love it! I have shot it alot in long range and palma matches. I am running 30.9grs of RL15 and getting over 2900fps with molied 107s out of a 28" Krieger. My key to getting 5+ firings out of the brass is I am running one of those Tubb CWS's in my rig. It really does save my brass.

Man....this is some great info! Keep it coming!

Jon

 

[nhm16]

FCB-
Are you shooting these 105s mag length or seating the bullet out further for single loading?

It sounds like the chamber is throated to so that when the Berger 105s are touching the lands, COAL is right at max mag length.

 

[Fried Chicken Blowout]

Sorry all I've been indisposed of since the flooding started here in Colorado helping support the medical needs of those involved. My house is high and dry but many, many people are not so lucky. It was quite an amazing week and very sad for those that have been displaced and the lives lost.

Thanks for the great thread and meticulous reporting!

BTW, what's the measured water capacity of fireformed Lapua cases in your barrel? With virgin 6.5G Lapua cases, I'm right around 35.1 and 1x-fired Hornady at about 36.0.

I'm going to be doing some loading today and I'll get you a case capacity on a formed Lapua case. From what I've heard the Lapua may be a much smaller capacity due to the thickness of the walls and or base of the case. After thinking about this, I think that may be why my shoulders look a little more rounded when fired. If the case wall is thicker it may not be able to form into the tight angles.

FCB-

Are you shooting these 105s mag length or seating the bullet out further for single loading?

I have had the 6FatRat for almost 2 years and love it! I have shot it alot in long range and palma matches. I am running 30.9grs of RL15 and getting over 2900fps with molied 107s out of a 28" Krieger. My key to getting 5+ firings out of the brass is I am running one of those Tubb CWS's in my rig. It really does save my brass.

Man....this is some great info! Keep it coming!

Jon

I load EVERYTHING at mag length. I have no interest in single loading. Unfortunately the chamber is not throated for mag length. I have a significant jump and there is a big difference between the two bullets I've used. The Nosler 105gr can't hold the same sub-1/2" group that the Berger Hybrids do so I'm assuming that's due to the Hybrids flexibility with the jump. I had stated that the Bergers could touch the lands at mag length early in the thread but I screwed up the measurement some how and that's not the case. The current jump to the lands of my load is 0.094" which is actually father than the Noslers that I had loaded but the Noslers didn't do as well. My current load COL is an average of 2.287" The mags measure just over 2.30 but that's not consistent between mags and if I let the average COL drift out much longer than 2.287" I end up with some meplats that are longer than others and they drag on the front of the mag. At this average I think my longest bullets are right at 2.294" and fit without issue. Lee made the suggestion to cut out the front of the mags to get more length which may be needed if I have the need to chase the lands. I might also be able to bend out of the front section of the mag some if I can do it in a clean way without breaking the welds. I've got the 20 round .223 body mags and I'm only using 11 rounds in them so cutting out the front of the top half of the mags might work since that area is supported by the lower receiver, but I might end up with a mag that blows all my ammo out all over the place if I drop it and that's not gonna work.

It sounds like the chamber is throated to so that when the Berger 105s are touching the lands, COAL is right at max mag length.

Sorry for the confusing info early on. I'll go back and edit that post at some point. See my reply above. Thanks!

 

[Fried Chicken Blowout]

Thanks for the great thread and meticulous reporting!

BTW, what's the measured water capacity of fireformed Lapua cases in your barrel? With virgin 6.5G Lapua cases, I'm right around 35.1 and 1x-fired Hornady at about 36.0.

Just measured 3 fire formed cases for water capacity. All of these were exactly 37 grs and all where once fired Lupua.

 

[McLarenross]

I wonder if you might do me a favor. Im going to build myself a FatRat when I get home and am trying to figure out my reamer specs and free bore. Could I ask you to take a base to ogive measurement for me at mag length for the 105 Hybrids? Like you, it does me no good to single load, so I want to keep the lands as close to the chamber as I can for minimal jump at mag length. Thanks in advance.

 

[Fried Chicken Blowout]

I wonder if you might do me a favor. Im going to build myself a FatRat when I get home and am trying to figure out my reamer specs and free bore. Could I ask you to take a base to ogive measurement for me at mag length for the 105 Hybrids? Like you, it does me no good to single load, so I want to keep the lands as close to the chamber as I can for minimal jump at mag length. Thanks in advance.

Here you go...

Berger 6mm 105gr Hybrid - Lot 5496
Lapua 6.5 Grendel case necked down to 6mm - Lot PH6020
COL - 2.285"
Base to Ogive with Hornady Bullet Comparator Inset 3-24 - 1.692"


What you will notice in my COL is that its much shorter than mag length. I've measured several mags and most measure 2.30 - 2.31 OAL just below the feed lips. But there are inconsistencies in the pinch weld that really make that unreliable as you load the mag. When I loaded out to a max of 2.30 I ended up being able to only load about 5 rounds before one of the bullets would drag. So I bumped them back to a MAX of 2.294 which gives me enough clearance that none of the rounds hang. The 3 rounds I pulled out of the box to measure were 2.285, 2.286 and 2.288 in COL the base to ogive of those three I measured were all within 0.001" of each other with the one I quoted above being in the middle. If I went through long enough and checked more I would find the ones that are 2.294 due to the inconstancy in the meplat. So while you could load longer you'll end up with mag issue. If anyone has advice on how to uniform the front of the mags so I can load out to 2.230 let me know.

My next purchase before i load the next batch on formed brass will be a bullet pointing and trimming system. This will totally uniform the meplats and resolve some of the inconsistency issue and allow the seating to be about 0.005" = 0.010" longer in theory.

If you want them measured with a different insert or need any other information please let me know. Also please pass along all the specs on the reamer and were we can order one "off the shelf" if we all so desired please.