Posts: 12
Threads: 2
Joined: Jun 2020
Hey guys,
Check my head for me here, I loaded some 75gr VMax with 29.5gr of Power Pro Varmint, and it would only extract them part way, or when they did eject it wouldn't pick up the next round. Brass is converted IMI 7.62x39, crono reading was 3080fps for that load. Factory Hornady Black 105 HPBT cycled fine and cronoed 2658fps. This is out of the 20" Monster barrel, A2 recoil buffer and spring, M16 BCG, accuracy was good with both loads, I took the 105gr all the way out to 600 yds on steel no problem, took the 75gr out to 300 yds before I got fed up with it jamming and not cycling.
So, ideas? Up the powder charge? Punt?
Greg
There it went.
Posts: 893
Threads: 35
Joined: Jun 2020
Lighter pills need more gas or less buffer/spring. That said your load is middle of the pack, hdy gas gun data goes up to 30.6, but that’s with hdy brass, yours is different. In the 20” I’ve been running about 120 faster than the hdy but that’s where your mv is... so you might well be at the top mv you ought to go for...
so idk, maybe buffer/spring?
Posts: 399
Threads: 35
Joined: Jun 2020
I have found that an LRP, relatively fast powders and light for caliber bullets in an x39 case requires backing off the charge quite a bit. More spark and a fast burn can result in substantially increased pressure. I start below published starting charges using LRPs in an x39. In my 6.5G, im currently running 85 grain Sierras in an x39 case with 26.5 grains of H322 at 2760 out of a 22". Hodgdon's starting charge is 27 in the low 2600s out of a 24"....
It looks like your load is hot ( the velocity is saying that) and your jams/non feeding are likely caused by the bolt cycling too fast. The bolt is likely slamming back before the case has a chance to clear the chamber, and when the case does clear, the bolt is moving too fast to pick up a round on the return. Does the bolt lock back on the last round? I would back off the charge a grain or 2. I've never used PPV, but it appears to be relatively fast according to "the chart"
Posts: 12
Threads: 2
Joined: Jun 2020
Bolt doesn't lock back on last round, case necks are sooty, and the primers are still round, no flattening at all. That is what has me confused here. I measured and case capacity was only .4 grs less in the X39 brass. I am using Remington LRP, they are middle of the pack as far as burn goes. But I will back off 1gr and see what that does. If it gets worse I will just wait until I have proper brass for it and just use this in the Grendel when hunting.
Greg
Posts: 237
Threads: 55
Joined: Jun 2020
Tried a carbine buffer and spring?
:: 6mmARC Target Cartridge with Hunting Capability :: 6.5 GRENDEL Hunting Cartridge with Target Capability ::
:: I Drank the Water :: Revelation 21:6 ::
Posts: 174
Threads: 17
Joined: Jun 2020
I have run into problems with converted brass in my bolt guns, either the shoulder was not sized back enough or the case base needed more (deeper) sizing.
If you have made dummy rounds out of your current load and cycled them by hand it may give some clues.
Posts: 893
Threads: 35
Joined: Jun 2020
Note, if you have an A2, you're probably using the rifle length stock... so use the extra carbine spacer if you use the carbine spring and buffer. I've done that and it works. Don't use a bare carbine spring/buffer in a rifle length tube.
Posts: 12
Threads: 2
Joined: Jun 2020
OK, went back out today and shot it with just the factory Hornady ammo, and it started doing the same thing.... So a little history about the BCG I am using, Way back in the day, I think it was the second Grendel board, BFT or someone had some AA fluted stainless barrels with bolts. Fast forward 10 years or so, I was using that BCG in the 6mm ARC until BFT gets in the new version of his bolts. Long story made short, the gas rings were worn almost away, part of one was gone. They were the same ones that were on the bolt back when I got it. So, 10 years of shooting, and only god knows how many rounds and they wore away. The carbon buildup on the tail of the bolt was nuts, there was a ridge where it seats in the carrier. New gas rings are on the bolt and it is nice and tight again, and I will bet that fixes quite a few issues with the cycling.
But yes I am going to back that load of in the X39 brass and see how it does. I know have 60 pieces of 6mm ARC brass from the range session the other day and today to reload with as well.
Greg
There it went.
