Gas Gun Precision Loads

[Reaper 31]

Hello everyone,
Trying to get some pointers on how to get my velocity spread down to what is "acceptable" on a gas gun. My current setup is a 22"criterion barrel (6.5 CM)with about 100 rounds +/-. I'm testing loads using the .2 grain increment method from 65 guys and using the 130gr Berger AR. I don't have my current data with me but im getting between 2670fps and 2720fps. Nothing consistent at all however grouped very well. All where loaded to magazine length.

Current brass prep and load method:
-FL Size with RCBS dies (tumble clean brass)
-Hornady Brass trimmed with L.E Wilson trimmer.
-K&M primer pocket correction tool
-K&M flash hole tool
- chamfer and deburr (45 degree chamfer head)
- CCI 200 with RCBS hand primer
- H4350 with Chargemaster Lite (can't remember grain charge)

I know it's not a bolt gun but looking to compete in PRS. I have a dedicated bolt gun for other disciplines but would love to run around with my gas gun. Any help would be appreciated!

 

[bfoosh006]

Consider using different primers, and testing them for results.

Nothing the matter with your choice of primer... but you might get better results with another brand.

 

[Reaper 31]

I'll try different primers. I'm wondering if it's worth to have Forster custom honed dies made for a gas gun?

 

[Sutherlandsd]

I honestly do hardly any prep at all for my gas gun stuff I tumble it and size it with a wilson sizing die and dump powder through a powder die with on a dillon 550 progressive using a chargemaster... I seat with a forster seater. I honestly dont even sort my brass on gas guns I just buy the shit hornady that people sell on the exchange. I occasionally will pick it up and load it again depending on how lazy I am that day.

I get usually single digit SD/ES or if it is double digits its in the low teens and I shoot 147 ELD-M pretty damn consistently .75moa or less all day at 2710fps using h4350 and cci 250 primers (damn the RL26 shortage...).

Sometimes doing more just gets you less.

I'll be honest I am not the berger fan that apparently the rest of the world is especially the 130 hybrid, I have gotten some absolutely embarressing lots of bergers lately. I would try a different bullet first. Your primer is not going to make up that big of a difference most likely. If you want to stay in the 130s try the eld-m its cheap enough to try. I have yet to see a rifle not shoot the 140 eld-m decent though, if you are lucky and your rifle likes the 147 its very nice and reasonable especially if you can get ahold of RL26.

 

[Sutherlandsd]

One thing I left out that I do on every piece of brass before it gets put in my dillon, I have a seperate redding T7 press with a sinclair expanding mandrel with an Oring to make it float that I use on every piece of brass to make everything start out on an even footing. If I dont use that occasionally I will get some wierd crap happen.

 

[Texascbr]

One thing I left out that I do on every piece of brass before it gets put in my dillon, I have a seperate redding T7 press with a sinclair expanding mandrel with an Oring to make it float that I use on every piece of brass to make everything start out on an even footing. If I dont use that occasionally I will get some wierd crap happen.

So I’m clear, you use an expander mandrel before resizing? I’ve always used the mandrel after sizing and curious if I’m missing something or you have found a better process? Do you also run through a mandrel a second time once you have sized?

 

[Sutherlandsd]

I use it before just to get the neck uniform and get out the dings on gas guns.

Edit

I use mine like you on my LR bolt guns it’s setup after sizing and before powder.

Edit 2..

I also use the sinclair on new brass before I ever size it (or on any "once fired" brass off the exchange).

 

[MontanaMan]

You don't say if the brass is new or has been fired or what you did to size the necks; my initial guess is neck tension variance.

MM

 

[Yondering]

You don't say if the brass is new or has been fired or what you did to size the necks; my initial guess is neck tension variance.

MM

That is my thought as well.

Also, I disagree with Sutherland's comment above about primers. A different primer can make a huge difference, and you won't know till you try.

Also play with seating depth if you haven't already, that affects both accuracy and SD and longer is not necessarily better.

My final thought, specific to a gas gun, is to make sure your gas system is tuned well for that load. If it's overgassed, as large frame ARs are so prone to, that can have an effect on both accuracy and SD.

 

[bfoosh006]

I don't think I'd go down the custom honed die set for a semi auto. Chambering is got to be smooth and easy in a S/A... with a bolt gun you can manually "cam" the round into place.

 

[bfoosh006]

Has anyone read the article Gary D. Sciuchetti, Handloader # 257.... "Developing an Accurate 308 Load"..... beyond a doubt, the most thorough reloading / component test I have seen.

Using a .308 SAKO TRG-22, 165-168gr bullets, a specific Varget powder charge weight ( 45.0gr ? ) and 168gr FGMM match as a standard ( grouped .375-.625 )

He recorded the difference in group size , between all the available reloading components
He tried every brand primer , every brand brass case, ( once fired and virgin ) fired said cases to the end of its useful life, every 165-168gr bullet available at the time, altered setting depth.... etc.

As an example... primer testing resulted in a 1/3" + difference in group size.
Powder charge weight differences...up to 3/4" +
Using different OEM cases .... 1/4"+
Neck sizing once fired cases... improved across the board
Brass endurance testing ...10 different brands and makes ( nickel cases ) full length reloaded and fired until case stretching caused a failure.
Accuracy with Bullet as the control Component ( 32 ) .... up to 2" differences
Various factory rounds, including Ball ammo, and Various USGI Match ammos
Seating depths of Solid Copper bullets could change group size by 3"
Component changes in POI

IM me if you are interested.

 

[Sutherlandsd]

I don’t think a primer can cause a spread of 50fps but I’m sure it’s possible. Neck tension seating depth or a bad lot of bullets would be my guess. I have had lots of Berger’s that would lay them one on top of the other at 100 yards and have an insane amount of spread. When I investigated the ogives where everywhere switched bullets and back to normal.

 

[Yondering]

I don't think I'd go down the custom honed die set for a semi auto. Chambering is got to be smooth and easy in a S/A... with a bolt gun you can manually "cam" the round into place.

Having a FL Forster die honed has no effect on "smooth and easy chambering" - they hone the neck to match your brass so it sizes correctly for the amount of neck tension you want, rather than typical excessive working of the neck. It's still a FL sizing die.

A honed die is just as appropriate in a gas gun as it is in a bolt action.

Also - don't make the assumption that accuracy and ES/SD correlates at any close/intermediate ranges. You can have very low SD numbers and terrible accuracy, or great accuracy and high SD. Velocity variation doesn't really correlate to accuracy until you're shooting long range, but even then a low SD number doesn't necessarily mean good accuracy.

Sutherland - I've seen the wrong primer cause spreads a lot higher than that. It does happen.

 

[bfoosh006]

Having a FL Forster die honed has no effect on "smooth and easy chambering" - they hone the neck to match your brass so it sizes correctly for the amount of neck tension you want, rather than typical excessive working of the neck. It's still a FL sizing die.

A honed die is just as appropriate in a gas gun as it is in a bolt action.

Thank you for the info, I didn't realize the Forster Honed Die was more neck oriented. That actually sounds like something I would be much more interested in.

 

[Reaper 31]

You don't say if the brass is new or has been fired or what you did to size the necks; my initial guess is neck tension variance.

I'll have to look at my neck thickness variation. All of my brass for the gas gun is Hornady. I know they get beat up so I didn't want to use higher $ brass. (I'm open to suggestions)
At what point do you switch brass on your load development? I was thinking of trying Starline SRP to see if that lowered my ES.

 

[Reaper 31]

As far as using an expander mandrel, do you simply remove the expander ball from your FL sizer and basically use it as a body die, then run the case through the expander? Does this help lower ES?

 

[bobke]

To first question, yes. To second, handful of factors will affect ES ie. neck tension, brass temper, etc, but given some control of variables, potentially-yes.

 

[larryh128]

That is my thought as well.

Also, I disagree with Sutherland's comment above about primers. A different primer can make a huge difference, and you won't know till you try.

Also play with seating depth if you haven't already, that affects both accuracy and SD and longer is not necessarily better.

My final thought, specific to a gas gun, is to make sure your gas system is tuned well for that load. If it's overgassed, as large frame ARs are so prone to, that can have an effect on both accuracy and SD.

I personally have had great luck using #34 CCI primers in my AR 6.5 C. Harder cup. Accuracy has been good using RL-17 or any other 4350 speed powder with 130's but I agree that the 140-147 gr ELD stuff shoots very well.

 

[larryh128]

I would be doing a neck turn clean up on your cases. My thoughts are it makes a bigger difference that some of the other steps. There are those who will tell you it's a waste of time in a Sammi chamber but they obviously haven't done it. I turn all my brass to .013 and that's enough.

 

[Reaper 31]

I personally have had great luck using #34 CCI primers in my AR 6.5 C. Harder cup. Accuracy has been good using RL-17 or any other 4350 speed powder with 130's but I agree that the 140-147 gr ELD stuff shoots very well.

I thought I was alone on using CCI 34s on a 6.5 I have good accuracy with my RDFs and RE 17 also.

 

[Reaper 31]

I didn't think neck turning on a gas gun would help, but I'm willing to try. I have the KM tool so I'll probably clean the necks up as mentioned. As far as expanding with a mandrel, do I keep FL sizing and testing loads, and chronograph velocity to see where I'm at? When will "I know" to change resizing methods?

 

[MontanaMan]

You're overthinking much of it, but you've gotten a lot of good replies & info here.

For load development as well as precision loads, I try to use only virgin or once fired brass for that work, all from the same lot & from the brand that I will use for precision work later in the same rifle, hopefully with low variance on neck thickness & similar hardness (springback, retetion, etc).

For those loads, even with new brass, I'll use a body die & then a Lee collet neck sizer..............the aim is as much uniformity in neck tension as possible. If you want to turn necks, have at it but I won't do it for even my best AR's.

Choice of powder can have some effect on velocity SD, whether it impacts accuracy / precision or not; generally powders that are on the slow side for the cartridge will usually be the worst offenders.

After that kind of work for load workup or precision testing & for loads that I want the highest precision from routinely, for bulk ammo I will just generally FL resize normally, keep brass by type as much as possible & keep the necks reasonably annealed if the firings get past 3-4. Those loads get a very light collet /factory crimp to also (at least IMO) help to have a little more neck tension uniformity.

For Fl sizing, I've always preferred Foster BR sizers & seaters going back to when they were Bonanza.

If you're only dealing with a couple of hundred brass, that's one thing; if you're dealing with thousands with various headstamps & lots, that's quite another matter.

MM

 

[Greg Langelius *]

Standard F/L die. Narrow base dies only if symptoms demand it.

.010"-.020" jump, OAL up to but not to exceed magazine length unless shooting single feed.

Faster powders, I use Varget a lot.

I avoid heavy-for-caliber bullets.

Initial increments 1% of max published charge, start 2% below max and work down. Continue working down and see if you can find a second node. Hotloading is not worth the trouble.

Do not exceed max published charge weights for 6.5 Grendel regardless of benign pressure signs. Other wider base cartridges for AR-15 may need similar precautions; ejectors suffer.

Floating firing pins and match primers may not like each other; I use Win primers for non-match applications, and for large volume (I.e. N/M Course) match applications.

My viewpoints can sometimes appear archaic; I started loading for semi's with the M1a in the mid 1990's.

 

[Sutherlandsd]

I simply refuse to turn necks even on my precision bolt guns. I think your overthinking it. I would check ogives on bullets first if they are consistent then I would look at neck tension; if all that checks out I would consider the primer.

 

[NCHillbilly]

I'm not shooting a 6.5cm, but my 308 loads saw a marked improvement in sd numbers just by seating the bullets a little (.025") deeper, instead of mag length. Doing so also slightly improved group sizes.

 

[Reaper 31]

I am seating bullet a tad under the book OAL 2.825 I believe for the RDFs but measuring ogive with the Hornady bullet comparator and i seam to only get .001 or .002 variance. I will be 100% honest I'm using the CE chronograph. The range I go to here as a good shaded area where it's not in sun. I have been contemplating the V3 chrony but I have read mixed reviews....

 

[Sutherlandsd]

If there is only that amount of variance I think you can rule out the bullet. I think you can add a big variable in your chronograph. V3 magneto is nice I switched to LabRadar and didn’t look back (I shoot other things besides rifles also). Both are a large step up over chrono with screens. Many threads on the pros and cons of each on this site.

 

[larryh128]

I simply refuse to turn necks even on my precision bolt guns. I think your overthinking it. I would check ogives on bullets first if they are consistent then I would look at neck tension; if all that checks out I would consider the primer.

Neck tension comes from a consistent thickness neck. It really make no sense to check every variable if the bullet isn't releasing the same all the way around the neck ; you are giving up accuracy. I've tested, even in gas guns neck turning to a consistent thickness results in much smaller groups. Will it take a 1" load to 1/2" ? No, but it will take it to 3/4".

 

[MontanaMan]

Neck tension comes from a consistent thickness neck. It really make no sense to check every variable if the bullet isn't releasing the same all the way around the neck ; you are giving up accuracy. I've tested, even in gas guns neck turning to a consistent thickness results in much smaller groups. Will it take a 1" load to 1/2" ? No, but it will take it to 3/4".

Thickness is not the only variable............brittleness / hardness / springback is also a huge factor especially if all brass in a group is not exactly from the same original lot with exactly the same number of firings.

MM

 

[Sutherlandsd]

Neck tension comes from a consistent thickness neck. It really make no sense to check every variable if the bullet isn't releasing the same all the way around the neck ; you are giving up accuracy. I've tested, even in gas guns neck turning to a consistent thickness results in much smaller groups. Will it take a 1" load to 1/2" ? No, but it will take it to 3/4".

if I shot bench rest I would turn necks. I don’t think my group size has no bearing on my ability to hit long range. I have rifles that shoot right at 1moa I have taken well past 1k with factory ammo. I have to weigh the time invested vs the outcome and neck turning has never been worth it to me. Ymmv to some it’s worth it.

 

[smoothy8500]

Trying to get my velocity spread down to what is "acceptable" on a gas gun. Nothing consistent at all however grouped very well.

How's the vertical spread at 300yds with the "good groups"? If it's good, how about at 800yds?

 

[larryh128]

if I shot bench rest I would turn necks. I don’t think my group size has no bearing on my ability to hit long range. I have rifles that shoot right at 1moa I have taken well past 1k with factory ammo. I have to weigh the time invested vs the outcome and neck turning has never been worth it to me. Ymmv to some it’s worth it.

If you do it once, and it only has to be done once, you will never look back. Easier than measuring ogives etc. I felt the same way as you until I did it once and compared the results not only on the target but at the chrono as well. I used to load hunting rounds for a very good friend, one day he showed up at camp with 3 boxes of Premium factory ammo and I asked him why he spent all that $. He stated this was Premium ammo and he knew they were all EXACTLY the same. A wager was made as I told him his premium loads wouldn't be within 50 fps of each other in 3 rds. Set up the chrono and I was wrong, they weren't within 75 fps. Then ran 3 of mine thru, 2 were identical and 1 was 1 fps faster. That's annealing, removing the burr on the inside of the flash hole, primer uniforming and neck turning. Consistent brass shoots good.

 

[Sutherlandsd]

I’m not disputing your results I shot bench for years, I turned necks for years. Without a doubt it will help your groups. Without a doubt though I can go to academy and buy a box of eldm for $25 and hit steel at 1200. Without a doubt I can reach in a bucket and pull out 20 random pieces of hornady brass that’s been once fired hit it with a Sinclair mandrel stick it in my Dillon and charge it with my chargemaster and cut the factory sd/es in half and surprise still hit steel at 1200 with a 5-7 minute time investment. To me it’s the law of diminishing returns vs my investment in time.

Plot twist I don’t anneal 6.5 creedmoor either the brass is so plentiful I rarely use it more than once or twice and I get the results I seek without it or the time investment. Hell I very rarely trim the brass. Case in point tomorrow I will hit the range with about 100 rounds of Valkyrie I will load tonight on my Dillon and use the Dillon to throw the powder it will still hit the steel with boring regularity and will take about 15 minutes of effort to load that 100

a lot of this is just what your trying to get out of your gun and how much you like to reload. Some people would rather reload than shoot that ain’t me. I'm past shooting bench rest so groups less than .5 moa don’t get my rocks off.

100% though you can get very small groups and single digit sd/es with a minimal amount of effort if you use your time wisely and have a good press and good equipment.

if your not getting the results you seek though then by all means adding steps may help your situation, turning necks is beneficial in that case as is countless other brass prep steps. My laziness should not be anyone’s guide, I’m just stating what’s possible with minimal effort.
if you put forth less effort than me you would be buying your ammo, somehow though when I miss it’s not my rifle or my ammo it’s still me.