6gt
- Thread starter Dthomas3523
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I don’t know when GAP will get more GT brass but I did speak with Alpha in December and they told me they are doing “a very large run” of GT brass in early 2022.
I've had some weirdness with 112gr Match Burners and 6.5 StaBall lately.
I've chrono'd this load at 2,948 fps @ 80 deg and 2,935 fps @ 35 deg. Then I went a week ago and groups opened up and I was at 3,011 fps @ 55 deg.... I did change a few variables, I was using a new batch of 112gr and I was using a new batch of GAP cases, which were within a tenth or two of my older brass in measured case capacity after firing. Hard to figure what would cause that kind of bump, maybe smaller starting case capacity on new brass? I don't think I've ever seen a difference that significant though.
I'm curious what mags folks are having good luck with, my MDT works well with under 8 rounds loads loaded, but I get nose dive with more than that, even after adjusting feed lips.
I've chrono'd this load at 2,948 fps @ 80 deg and 2,935 fps @ 35 deg. Then I went a week ago and groups opened up and I was at 3,011 fps @ 55 deg.... I did change a few variables, I was using a new batch of 112gr and I was using a new batch of GAP cases, which were within a tenth or two of my older brass in measured case capacity after firing. Hard to figure what would cause that kind of bump, maybe smaller starting case capacity on new brass? I don't think I've ever seen a difference that significant though.
I'm curious what mags folks are having good luck with, my MDT works well with under 8 rounds loads loaded, but I get nose dive with more than that, even after adjusting feed lips.
@Gtscotty
I wouldn’t call that weirdness. You changed two variables. Back it down and build your charge back up to where it shoots good again. It should be pretty close in speed to what you had before. Provided you fall between the 35° and 80° you tested at before. It may not be the exact same speed as the cases and bullet has changed, but it should be ball park.
If you haven’t cleaned your barrel in a long time that could be a contributing factor as will. If you clean it give it ten rounds or so to start settling in before doing any load development.
I wouldn’t call that weirdness. You changed two variables. Back it down and build your charge back up to where it shoots good again. It should be pretty close in speed to what you had before. Provided you fall between the 35° and 80° you tested at before. It may not be the exact same speed as the cases and bullet has changed, but it should be ball park.
If you haven’t cleaned your barrel in a long time that could be a contributing factor as will. If you clean it give it ten rounds or so to start settling in before doing any load development.
Hmm, I call it weirdness because I've been loading a bunch of different chamberings for a while now, and I've never seen a bullet lot change jack pressures like that. For reference, that's the same velocity that 40.3gr (0.8gr more) of StaBall gave me at 80 deg (25 deg warmer). I've used two other lots of this bullet, and there was no noticeable difference in velocities between them.
A new lot of cases with significantly lower capacity could definitely jump pressures, but I checked the water capacity on these when I got back, and trimmed the same they *may* be 0.1gr less... not nearly enough difference to explain what I measured. That's why it's weird to me, the only other thing I can think of is maybe the new cases are significantly undersized until they get blown out in the first firing, and are changing the powder burn characteristics quite a bit? Still seems like a lot though.
This barrel only has 300-400 rounds on it, and has honestly been surprisingly picky, but I guess I can't rule out a ring. I've cleaned pretty regularly, but I should probably break out the bore scope and check things out.
I did try some RL16 (my all around favorite medium rifle powder if I had to pick one) with the 112gr. Groups weren't impressive at the lower loads, but started to come together at 36.7gr and 37gr. More work to be done in that area, but here were the (only one shot) velocities:
112gr MB, Hornady Gap cases, 450s, 60 thou off the lands. 23" PVA prefit.
RL16
35.8gr - 2,849 fps
36.1gr - 2,887 fps
36.4gr - 2,874 fps
36.7gr - 2,915 fps
37gr - 2,901 fps
I Chrono'd 37gr of RL16 in the old cases with an older lot of bullets on the same 35deg trip mentioned above at 2,895 fps. So same components shift as with the StaBall load above didn't really change much, certainly not a 70fps change.
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Something has changed enough to give you a lot more pressure, that much is known. The hard part will be running it down.
Was load development done on a new barrel or after a couple hundred rounds? Maybe the barrel has sped up?
I've not shot StaBall, but I have gone through a few jugs of RL16. I learned the hard way with it to stay on top of cleaning or pay the price with carbon rings. I've heard StaBall is dirty, but I don't know about carbon rings. Maybe your bore scope will have some answers for you?
Was load development done on a new barrel or after a couple hundred rounds? Maybe the barrel has sped up?
I've not shot StaBall, but I have gone through a few jugs of RL16. I learned the hard way with it to stay on top of cleaning or pay the price with carbon rings. I've heard StaBall is dirty, but I don't know about carbon rings. Maybe your bore scope will have some answers for you?
I'm running 5, 10 and 12 round MDT mags with my GT and I don't have any issues. I'm using an MDT ACC and a ARC Nucleous action. I have shot 109s and 105s mostly. I tested some 112s this summer but didn't get the results I was looking for and went back to Bergers. I wouldn't think 3 or 7 grains would make a difference on the way the mag feeds? Have you ran lighter bullets?
One hole with 109, 108, and 112. Just different seating depths. 0.050 for 112 & 108. 0.060 109’s. I use the MDT polymags. No issues except the first round am the do have the mag extension. Just takes a bit more umph. Like anything else can’t load mag against berricade
I've never been able to get MDT mags to run in my GT's.
AI or ARC seems to run well for me.
AI or ARC seems to run well for me.
It’s all in adjusting and tuning the feed lips. I’ve spent hours getting them just right, fighting down my notes, and repairing them after I’ve squished them.
If my options are spending hours playing with feed lips, or buy a different mag that works out of the box, I'm going to buy a different mag.
To each their own, I guess.
I would say development was done over a couple hundred rounds, lol. The 80 deg velocities were early on, but the others were all recent. Searching for a consistent load with this rig has been more of a struggle than I'm used to, but I've primarily been using the 112gr with a couple unimpressive sessions of 108gr ELD sprinkled in, so maybe that's the problem... I saw that Proof is going to start making 6GT Origin prefits, so maybe I'll just pick up one of those when they come out and see if that clears things up.
I need to find some Bergers, I heard there was supposed to be a batch of 105gr Hybrids shipping soon, but I haven't seen anything. I don't think the bullet weight is having any effect, the nose dive is a mag issue, and I thought messing with the feed lips would fix it, but it didn't, maybev I'm just not there yet. I have a Magpul mag that never has nose dive, but this rifle over runs the case head pretty often with that mag, weird thing is that mag also caused the same malfunction in my old RPR in 6.5.
Maybe your mag isn’t positioned optimally with your chassis/action combo? Do you have a lot of for/aft wiggle?
Hmmm maybe I'm reading it wrong, but 1.725" - 0.020" = 1.705"? That is 0.015" shorter than the 1.72" trim length in Hodgdon data. Or do you trim to 0.01" under max?
I worded my post incorrectly, the max length is .005 longer than what was originally put out. I've never looked at hodgdon's information. Originally it was 1.720 - .010.
On my 4th barrel. 2 back-to-back matches next month to burn her in. So far, so good. Dropped some speed on a new jug of Varget.
Get ahold of MDT. They reached out and sent me new followers, mag springs, and spacers to alleviate the issues I was having. Make sure you tell them if you have binder plate or non binder plate mags. Also, let them know if you have 10 or 12 round magazines. They will send the proper sized spacer for them.
The only downside so far is that I have to load to mag length and under to find my optimal seating depth. This knocked off about 60 thou of play room off the lands for me.
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I'm not sure how to continue to be polite and say I don't run MDT mags in my GT because they don't fvcking work.
AI Mags, ARC mags, take out of package, insert bullet, go to range.
Rinse, repeat.
No calls. No email. No swapping. No tweaking feed lips. No searching who else has the problem.
Apologies in advance for jumping from the current topic on this cartridge.
Anyone have experience running 115 DTAC's? Just fire formed cases and about to get into load development.
HH barrel (7.5"twist)26", Alpha brass (current GEN), GMM primers, H4350. I want to be able to compete at 1k with this cartridge. I haven't chrono'd anything to this point. From what I can see, the 105 to 108 grainers seem to be the best performers to this point.
I guess I'm wondering if the 115 is simply too heavy. F-Open is the disclipline.
I could always designate these for 600 matches only. Just wanted some feedback from those who've gone the 115 DTAC route? Thanks
Anyone have experience running 115 DTAC's? Just fire formed cases and about to get into load development.
HH barrel (7.5"twist)26", Alpha brass (current GEN), GMM primers, H4350. I want to be able to compete at 1k with this cartridge. I haven't chrono'd anything to this point. From what I can see, the 105 to 108 grainers seem to be the best performers to this point.
I guess I'm wondering if the 115 is simply too heavy. F-Open is the disclipline.
I could always designate these for 600 matches only. Just wanted some feedback from those who've gone the 115 DTAC route? Thanks
DTACs will work fine for the 6GT.
They have some inconsistencies in the past, but it may have been fixed.
They have some inconsistencies in the past, but it may have been fixed.
That may be for you, but I have had zero issues with 5, 10 and 12 round MDT mags. I have some shooting buddies that use AI mags and they’ve modified them to suit their needs. They modified the feed lip angles and cut the lips shorter.
I have used other mags in another gun and had to modify the lips to feed. I did what was needed to make them run.
I don’t think it’s as easy as saying they never work or always work. There are so many combinations of cartridges, actions and chassis/stocks that no one brand is the end all be all.
I’ve been shooting GT pretty much since it’s inception. I’ve always ok h ever used AI and Accurate mags. I’ve never had any issues with them feeding. Coincidently, pretty much everyone I do see having feeding issues are all with MDT mags. Just sayin 
A lot of issues can be traced to the bottom metal or chassis, in some cases. In my experience, I have used Magpul, ARC, AICS, AW, and MDT mags for multiple barrels. The only issues I had were associated with a Gen 1 and Gen 2 Manners Mini chassis. I have had zero issues over many barrels with Hawkins or OTM M5 dbm.
I'm sure some are, but my mag issues aren't bottom metal related. I'm using an MDT mag in an MDT chassis, but I can see the top round nose diving just holding the loaded mag, when I strip one off either with the bolt or by hand, it will do the same thing until I get down below 8 rounds in the mag. I didn't notice earlier because I was only loading 5 for most of the load development. Messing with feed lips hasn't really helped yet, it seems like friction in the mag body is keeping the top round from pushing up against the lips sufficiently, and I've cleaned the mag with one shot, which usually slicks things up pretty well.
Seems like the reviews have been mixed on ARC mags feeding reliably, maybe Accurate would be a safe bet to try next.
I've only used accurate mags and they feed without any tweaks
Accurate-Mags work well for me in a ACC Chassis. Still had to open up feed lips slightly for smoother feeding.
Not to beat a dead horse, but...
Like most everyone else, I had trouble feeding 6GT with MDT mags. I was not surprised as it was a known issue when I started shooting the cartridge. I asked MDT about it and this was the response:
In my experience, no amount of feed lip tuning will completely resolve the issue without creating another issue. The Dasher/BR mag kit will limit your OAL to 2.505" which is way to short for me (standard freebore).
Accurate mags work fine, but did require some minor tuning to feed smoothly in my case.
Like most everyone else, I had trouble feeding 6GT with MDT mags. I was not surprised as it was a known issue when I started shooting the cartridge. I asked MDT about it and this was the response:
In my experience, no amount of feed lip tuning will completely resolve the issue without creating another issue. The Dasher/BR mag kit will limit your OAL to 2.505" which is way to short for me (standard freebore).
Accurate mags work fine, but did require some minor tuning to feed smoothly in my case.
+2
I spent a lot of time trying to tune my MDT mag and it just wasn’t there. I had 4 and 2 ran fine, 2 did not. All 4 purchased at the same time. I hit them up and got a dozen questions, I’m like but 2 are good and 2 are not… I don’t quite think it’s the chassis or action.
I ended up shifting to accurate and they ran my GT fine.
I tried the plastic MDT mags and they absolutely did not work for my GT. However a friend has used them and had no issues… we run the same chassis and action.
Oddly I had similar issues with MDT and their BR mag. Some worked and some simply did not.
The accurate mags are actually cheaper than MDT mags now. Natchezs has them for $63.
I have run nothing but arurate mags and I haven't had to mess with a thing
Part# 1000040 = no binder plate - max OAL 2.950"
Part# 1000009 = with binder plate - max OAL 2.875"
I use the mags with the binder plate and haven't tried without. I have friends who prefer the no binder plate version. I am not sure if it makes a difference for 6GT because I don't think you can load it beyond 2.875".
Both are 10 round mags that will only fit 10 round of 6GT.
Part# 1000009 = with binder plate - max OAL 2.875"
I use the mags with the binder plate and haven't tried without. I have friends who prefer the no binder plate version. I am not sure if it makes a difference for 6GT because I don't think you can load it beyond 2.875".
Both are 10 round mags that will only fit 10 round of 6GT.
The following data collected at 1,400 rounds on a 26" Benchmark VCC. Velocity has slowed substantially, which could be due to a variety of factors including throat erosion, brass prep, different lot of powder, weather, etc. These are 5 shot sample sizes. I ended up running 32.9 gr which averaged 2,830 FPS over a larger sample size.
Berger 105 gr Hybrid
Varget (32.2 gr to 33.4 gr)
CCI 450
GAP Hornady Brass (3x fired)
+/-0.060" jump (1.919" CTBO)
26" barrel, 1:7.5" twist
Temperature: 57
Humidity: 25%
Pressure: 27
32.2 gr Varget
Ave MV: 2,785
ES: 30
SD: 12
32.4 gr Varget
Ave MV: 2,793
ES: 34
SD: 14
32.6 gr Varget
Ave MV: 2,809
ES: 12
SD: 4
32.8 gr Varget
Ave MV: 2,819
ES: 22
SD: 9
33.0 gr Varget
Ave MV: 2,833
ES: 16
SD: 7
33.2 gr Varget
Ave MV: 2,857
ES: 26
SD: 12
33.4 gr Varget
Ave MV: 2,875
ES: 37
SD: 18
Berger 105 gr Hybrid
Varget (32.2 gr to 33.4 gr)
CCI 450
GAP Hornady Brass (3x fired)
+/-0.060" jump (1.919" CTBO)
26" barrel, 1:7.5" twist
Temperature: 57
Humidity: 25%
Pressure: 27
32.2 gr Varget
Ave MV: 2,785
ES: 30
SD: 12
32.4 gr Varget
Ave MV: 2,793
ES: 34
SD: 14
32.6 gr Varget
Ave MV: 2,809
ES: 12
SD: 4
32.8 gr Varget
Ave MV: 2,819
ES: 22
SD: 9
33.0 gr Varget
Ave MV: 2,833
ES: 16
SD: 7
33.2 gr Varget
Ave MV: 2,857
ES: 26
SD: 12
33.4 gr Varget
Ave MV: 2,875
ES: 37
SD: 18
Breaking in my barrel. 35g H4350, 108 BT .0020 off the lands, CCI 450s, Alpha OCD virgin brass. Groups have been very good. ED/SD are all over the place. From 8/3.6 to 43/16.7. I'm at 100 total rounds fired and no signs of speeding up yet. What kind of change in FPS should I expect to see when it begins to speed up? Is it incremental over a period of rounds? Or does it just get faster over several rounds?
2805 avg. 24 ED/ 10.6 SD
2805 avg. 24 ED/ 10.6 SD
I'd break in 36.5gr of H4350 with Alpha brass. One of the nice things about 6GT is there's pretty much no reamer variations. I'll wager you final charge weight will be around 36.7gr going 2900fps using Alpha brass.
Have you found it easy to get low SD’s with H4350 in the GT? Does it have a wide node?
I'm about ready to go load 50 rounds to shoot tomorrow for more break-in. Rounds 101-150. I'll vary some load weights and work up to your recommendation quickly and see how it goes. Hopefully we'll see her speed up a bit and I can 'try' to get some load development done for Raton next Sunday. Thanks for the recommendation.
GT is probably one of the most forgiving cartridges to load for. Super easy.
2 different 6gt barrels, not as easy as a dasher, bra, or br, but def not picky. 36.6gr H4350 with 109s 40k off lands shoots 4" at 870y thats the furthest I've shot paper. I think last time i ran 15 over chrono I had an es of 13, avg was 2907fps. I'm running a 28" bartlein 7.5tw.
Again, 6GT has almost no reamer variations. Follow this guy's load:
36.5gr to 36.8gr of H4350. 105gr to 109gr projectiles. .030 to .050 off the lands. Painless.
