I purchased two ammo cans of the American Gunner the other day and shot it in my new 12.7 Faxon group buy pistol as part of the break in procedure and noticed some signs of over pressure. There is a pretty good indention in the base of the case from the ejector hole. I purchased a chronograph and tested it today with one shot and it showed 2922 FPS and it left another good size indention in the case.
I also decided to test the 123 SST and it showed 2571 fps with no signs of over pressure. This doesn't make much sense to me, these kind of numbers from the 12.7.
The pic is a case from the AG and one from the SST. Please take a look and let me know it is a concern or not.
SST COAL is 2.241 with 1.668 ogive
AG COAL is also 2.241 with a 1.69 ogive
Not sure exactly what is going on but wasn't expecting this kind of velocity out of the 12.7.
I have an Odin Works 18" I can test the AG in but I believe the chamber is shorter than the 12.7 and I am worried it will also show signs of over pressure.
All I have ever shot out of my grendels has been SST, Black and some wolf. I have also recently purchased 5 boxes of AA 123 Lapua Scenar (1.71 ogive) from a friend and now I am worried these two will also show signs of over pressure. I have a lot of money tied up in ammo that may not work in my grendels.
I guess I need to measure my chambers to see if they could be short.
I can't see either, but it sounds like your chrono may not be working right. 2922 fps is long barrel 6.5 Creedmoor speeds for 123s. If it really was that fast, you're lucky to be in one piece. Have you finger seated rounds in the chamber to see if they'll drop out freely?
I thought about the magnetron as potentially not reporting the velocity accurately and it is very much possible. I did run a test with 22lr standard velocity (1070 fps) and it measured 1055. This doesn't eliminate the chronograph entirely since the Grendel was the first time I used it. Could be a setup issue with the Megatron. Also I only did one shot to test the velocity. Didn't have time for more.
Apart from the chronograph, the fact that the AG is exhibiting ejector marks, that should be enough of a sign that I have an issue with over pressure. I am green with all of this and will rely on the experts of the forum to help analyze. I will try to get more pictures.
Also the fact that relatively speaking, the SST was 2517, and I would expect something around 23 to 24 could also be a clue in solving the mystery.
Yes the bolt is the monster group buy bolt. The AG cartridge will drop in and out. Also tested the AA 123 Scenar with a 1.71 ogive and it also dropped right out so I don't believe I am in the lands. Funny thing is my Odin works barrel, the scenars will not drop out so it must have a shorter chamber than the faxon. I am going to measure both however.
07-08-2018, 10:20 PM (This post was last modified: 07-08-2018, 10:31 PM by sneaky one.)
Looks to be a lil warm gren nub--- return your chrony. It has to be 12-13 ft. away from muzzle, btw.
Quite the ejector swipe. Explain the rest of the evidence that u noticed.
I had a chrony unit fail on me.... Magneeto speed is good. Once the sensitivity is dialed in. H1 is good.
This is how AR bolts lose a lug. You do not want to lose lugs, or bbls.' or any part of You.
I have only blown 1 primer in my loading years- it was only due to a bad magazine, that ended up pushing a bullet in too far while going into te chamber. Angles- I'm a bridge engineer at heart.
Thanks to everyone who has responded. Sorry for getting worked up but man I was worried there for a few. This was the first shots out of the 12.7 and it had me concerned.
Good news, I went back out today and tested the Magnetron and I believe it was a config issue. The sensitivity was as high as it could get, I reduced it to normal. I also worked on reducing the spacing between projectile path and bayonet as I noticed the first time around it was a little larger than it should have been, maybe 1/2 inch. I then retested at arms length and empty mag well. The results were a lot more predicable.
For the first shot out of the 12.7 Faxon I used the 123 SST and only shot it once for comparison purposes, it went 2157 fps. After the change in chrony readings I felt a little better. The 123 gr AG 2 shot average was 2187 FPS. The AG still did show ejector marks even though it was about 30 fps difference. I also tested a different BCG, a fail zero and it still had the ejector mark. I believe I will check head spacing of both the SST and AG and see if there is a difference.
For the 18" Odin Works, one shot each, 2501 fps for 123 AG and 2424 fps for the 123 SST.
Sorry for crying wolf but it had me worried after seeing the ejector mark and the chrony speeds.
Shooting the AG may not be worth the risk in the 12.7, it is a little hot. I am working on a plan for load development now. The 12.7 will be hunting only. I am looking at the 100 Nosler BT and 123 SST, I'll see which one shots the best.
