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Old May 13, 2019, 08:01 PM   #1
CarJunkieLS1
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Heard of the GPC line?

Today I got to put some rounds through a new cartridge in development. It's an AR-15 cartridge made by MDWS called the 25 GPC. It's a 6.8spc case that's had the shoulder angle blown out and forward upping powder capacity.

I was using fresh brass simply ran through the sizing die and loaded. A 75gr HP at 3200 and a 85 Nosler BT to over 3100. Still working on cycle issues (gas port) but had no pressure signs. Velocity achieved with a 22" barrel.

So all you quarter bore fans are you as excited as I am to see what she'll do with 100 grain and up for deer.
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Old May 14, 2019, 09:22 AM   #2
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No. The extra powder the GPC holds is not enough to make a difference in the performance of the cartridge in IMO. But that only applies to my thoughts about the 6.8 GPC. Mark's family of GPC wildcats make for some interesting wildcats if you like playing around with wildcat cartridges. And if Mark is successful in bringing a metal mag to the Six8 market, I'll take my hat off and I'll give him kudos for that feat.

Last edited by ed308; May 14, 2019 at 09:38 AM.
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Old May 14, 2019, 01:02 PM   #3
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No. The extra powder the GPC holds is not enough to make a difference in the performance of the cartridge in IMO. But that only applies to my thoughts about the 6.8 GPC. Mark's family of GPC wildcats make for some interesting wildcats if you like playing around with wildcat cartridges. And if Mark is successful in bringing a metal mag to the Six8 market, I'll take my hat off and I'll give him kudos for that feat.
I agree that the extra powder capacity doesn't add much on the larger bores of the GPC line to make much difference, but IMO the smaller 6mm an 25 cal bore on that case offer a pretty sizeable increase of performance over the 6x45 and the 25-45.

I'm a AR fan and a quarter bore fan and I just like the added performance over the .223 based cartridges. And I really want to step up my AR-15 performance a few notches I've got the 7mm Valkyrie.
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Old May 14, 2019, 01:59 PM   #4
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Doesn’t excite me, but to each their own.
Variety is rarely a bad thing...
I get the performance to suit my needs with what is already out on the market and has off the shelf ammo available at decent prices.
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Old May 14, 2019, 04:05 PM   #5
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Factory off the shelf ammo just get me excited and I can always load better than what I can pick off a shelf.

If factory ammo suits your needs by all means go for it, I like oddball stuff and then seeing the look on people's face when the ask what I'm shooting and I say I'm shooting an AR other than 5.56, 300blk, or .308
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Old May 14, 2019, 07:56 PM   #6
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So you do it to “impress” other people, or what am I missing?

I hand load as well, but I don’t competition shoot of any kind so I have no need to squeeze any more performance out of my ammo than what I can already buy. Plus, for what I load, right now, there really is no cost savings either. My rifle already prints .4” 5-shot groups at 100 yards using factory ammo. If I hand load it might shoot .3”. Doesn’t get me excited.

I make it a point to not buy any gun that would require only hand loading. If there isn’t factory ammo available, and a decent variety, I’m typically not interested until/unless there is factory ammo. If a rifle won’t shoot some variation of factory ammo to sub-MOA, it doesn’t stay.
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Old May 14, 2019, 08:54 PM   #7
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I'm a AR fan and a quarter bore fan and I just like the added performance over the .223 based cartridges. And I really want to step up my AR-15 performance a few notches I've got the 7mm Valkyrie.

Love the 7mm Valkyrie. Almost bought one but got the 270AR sister cartridge instead since I have tons of .277 bullets. That is my only wildcat now after I sold off my TAC6 (6mm wildcat). H's 270MSR with the use of Dasher brass gives similar performance but requires less work and time to form the brass. I love wildcats but don't have the time to mess with them.

Last edited by ed308; May 15, 2019 at 08:05 AM.
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Old May 14, 2019, 09:51 PM   #8
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No I shoot oddball cartridges because I like being different and the standard ones are just boring. Factory ammo is boring and "my rifle shoots .4 5 shots with factory ammo" so now who's bragging...

And I almost got into the 270 AR but I'm a huge 7mm fan too and I stumbled on the Valkyrie, a few phone calls later and I had everything I needed to go 7mm Valkyrie even got 200 pieces of brass already formed so it loads like any other caliber.
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Old May 15, 2019, 07:15 AM   #9
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I was bragging, on the fact my “boring” rifle/caliber/factory ammo shoots so well and there is no extra performance gain to be had. The caliber started off as a wildcat hand loaders cartridge that proved itself to be better than current factory offerings. Big mfgs got behind it and started producing factory rifles so chambered and ammo that yields said .4” 5-shot groups.

So as I said before, wildcats don’t interest me until/unless they get to a point where there are factory offerings for ammo and to some extent, rifles. But they also have to perform better than other similar factory offerings or fill a void.
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Old May 15, 2019, 12:01 PM   #10
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"...Velocity achieved with a 22" barrel..."

I guess my 12" 6.5 Grendel and I will just watch... y'all have fun, though.
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Old May 15, 2019, 01:50 PM   #11
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"...Velocity achieved with a 22" barrel..."

I guess my 12" 6.5 Grendel and I will just watch... y'all have fun, though.

So enquiring minds want to know, what velocity you seeing with that 12" Grendel.
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Old May 16, 2019, 11:40 AM   #12
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I have no idea, I don't own a chronograph anymore... but on-line reports generally get just under 2200 fps for the Hornady Black (123gr), and around 2350 for the Wolf Classic (100gr).

Here's one report... skip to about 6:30 for velocity data.

https://www.youtube.com/watch?v=avC7P2ll2TM
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Old May 16, 2019, 12:19 PM   #13
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While at point in life where have enough projects to last, am appreciative of people continuing to push the boundaries/purposes/how to of cartridge development. Especially in the ar's, where the more information/variety the better. Got to meet some of these people last year at their get together, and they be good people.
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Old May 16, 2019, 01:50 PM   #14
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Originally Posted by 9x19 View Post
I have no idea, I don't own a chronograph anymore... but on-line reports generally get just under 2200 fps for the Hornady Black (123gr), and around 2350 for the Wolf Classic (100gr).

Here's one report... skip to about 6:30 for velocity data.

https://www.youtube.com/watch?v=avC7P2ll2TM
A 123 at 2220 from a 12" guess I'll just keep my 10.5" 7.62x39 and have a larger diameter exit too...and that garbage wolf FMJ ain't worth shooting.

And Zeke speaking of projects once I finish this one up myself and a friend will be doing 12" 8mm Kurz in an AR-15 pistol that should be a fun one to get working right.
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Old May 17, 2019, 08:01 AM   #15
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...and that garbage wolf FMJ ain't worth shooting.
Oh, my! Now I'll just have to stop shooting it..... maybe...... nope.

Quote:
...a larger exit...
did you say?

Then I'll see your .311" and raise you a .450 Bushmaster.



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Old May 17, 2019, 12:40 PM   #16
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A 123 at 2220 from a 12" guess I'll just keep my 10.5" 7.62x39 and have a larger diameter exit too...and that garbage wolf FMJ ain't worth shooting.

And Zeke speaking of projects once I finish this one up myself and a friend will be doing 12" 8mm Kurz in an AR-15 pistol that should be a fun one to get working right.
Lol. Your 123 7.62x39, given the same length barrel is slower, has less energy, and more drop at any range. Using the 1000ftlb of energy on target rule, The 6.5 has actually double the range of the 7.62x39. So the “bigger hole” won’t matter if it doesn’t have enough energy to make it to the other side. I’d take the 6.5 any day over the 7.62x39. Much better selection of bullets as well...
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Old May 17, 2019, 12:42 PM   #17
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You have fun with that 450 BM I'm not afraid to admit thats more recoil than I want to take. I shot the 25 GPC again today and a 100 Sierra went 2850 and a 85 Nosler went 3050. There's more room in it I haven't hit max yet. I am running out of powder capacity on the fresh cases. I'll have to see where I can get with formed ones. The formed cases hold 35.3gr of H20
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Old May 17, 2019, 12:47 PM   #18
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Well I know my 10.5 will shoot a 123 faster than the 2200 he gets. And the .310 SST. 310 Speer Gold Dot, and. 310 Hornady Soft point all work very well at 2500fps and down to 1900-2000 and less. At the ranges these short pistols are ethical on deer at the BC of the sleeker 6.5 bullets just don't make a hill of beans difference.
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Old May 17, 2019, 01:35 PM   #19
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You’re right, everything you have is the best, you’re the best, and you are the only one who can hand load to gain performance over factory ammunition. His factory ammunition runs 2200 FPS and you want to compare it to your hopper up hand loads at 2500 FPS. The 6.5 can be hopped up ad well and still keep the performance advantage gap over the 7.62x39. So, again, all things being equal, the 6.5 has and keeps a clear performance advantage over the 7.62x39. But wait, my 12” barreled 7.62x51 can’t be touched by your 7.62x39 or the 6.5 at any bullet weight...

Have fun
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Old May 17, 2019, 01:48 PM   #20
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Quote:
Quote:
...and that garbage wolf FMJ ain't worth shooting.
Oh, my! Now I'll just have to stop shooting it..... maybe...... nope.

Quote:
...a larger exit...
did you say?

Then I'll see your .311" and raise you a .450 Bushmaster.



Y'all have fun!
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Tsk tsk tsk...you coulda had a 458 socom.

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Old May 17, 2019, 01:58 PM   #21
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This is where someone inserts their 50 Beowulf as another one up...
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Old May 17, 2019, 02:00 PM   #22
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This is where someone inserts their 50 Beowulf as another one up...
Probably not--since the 458 socom is better than either of them.

Oh oh..did I really say that?
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Old May 17, 2019, 02:29 PM   #23
CarJunkieLS1
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The 2500fps I quoted is Russian steel case 124 fmj factory load from a 16" barrel, my personal 6.5 Grendel gets Hornadys factory load at 2475 in a 20" barrel. That's factory to factory.

I never said I had or was the best. Sorry you saw it that way. Just when it comes to carbine length and shorter pistol barrels the 7.62x39 IMO has an advantage over the 6.5 Grendel. Same case basically same weight bullets used most of the time, same powder capacity. At the ranges the short pistol barrels are ethical to use on deer the Grendel just doesn't have any real advantage over the 7.62x39. If we are shooting paper or steel at 300 yards or more I'll give you that one.
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Old May 17, 2019, 02:40 PM   #24
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Again, apples to oranges. 16” barrel vs 10.5” SBR. You’re very good at the one up game when all things aren’t equal.

You’re wrong, the Grendel has more speed, and energy, with less drop and EVERY ballistic calculator will confirm this. So the 7.62x39 is at a disadvantage in all scenarios in all barrel lengths and all bullet weights. Look it up, run the numbers yourself.
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Old May 17, 2019, 03:12 PM   #25
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I actually compared a 16" to my personal 20" so there's that. Not a 16 to a 10.5 like you stated. Run the numbers both cartridges in a short barrel say both 12" and there is not a single advantage that matters inside of 200 yards(max distance they are effective on deer). I know Grendel is king in AR-15 and anyone who says it or shows otherwise is being unfair...its alright I get it.
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