224 valkyrie neck tension

[bgblue1978]

I have a 224 valkyrie upper built by dtech. It shoots factory Hornady 88s consistently sub moa for 5 shot groups. I've started loading for it with Hornady 88s, berger 85, berger 80.5 in new starline brass. Only tested varget so far but planning 4895 next.

The first time I loaded with new brass I used a Redding sizer with expander removed and sinclair expander mandrel, mandrel measures .222 and got pretty bad groups. 4th and 5th shots got progressively worse so I suspected insufficient neck tension. I shot same load again with a slight crimp and got back to back .6" groups. So my question is should I just do future powder/projectile testing with the slight crimp or is it worth getting more mandrels to play with different neck tensions?

Edit: I should add that when I shot the crimped load I also tested without crimp and measured OAL of the 5th shot and it was growing about 3-6 thousandths. And all shooting was magazine fed shot off harris bipod and rear bag.

 

[searcher]

What you want is to size your brass down with a bushing that is about .005" smaller than the measurement on the neck as close to the mouth as you can repetitively measure - and this should be done on a piece of prepped brass that has a seated bullet in it. As you will usually get about .001" of "spring-back" on your necks after sizing them (this full spring-back can take a day or more - so best to just allow for it automatically in your measurements), that will leave about .004" of a reduction to hold your bullet from slipping. Sometimes, I use only .004" smaller, though that is when I am not using moly or HBN coated bullets - or when using long bullets that take up the full length of the neck for contact - such as the bullets you are using. You might find it necessary to get a bushing on either side of the one you think you need just so you have on hand if needed - which seems to be quite often.

When crimping for an A/R, achieving better accuracy than a non-crimped bullet that is adequately tensioned is VERY tough to do. I expect better than .6" MOA out of my A/R's that are shooting cheap varmint bullets. I'd expect WAY better using those premium bullets. Rather than messing with mandrels (assume you are using to compensate for over-sized necks?), I'd turn the necks to where all but maybe 3% of your cases are showing about 75% clean brass. Then, sized with the appropriate quality full-length bushing die, you can achieve about as good of consistency as you are going to get. Running a mandrel into them is not needed to get down to half what you are getting unless you have a bad press, die, etc. - which is a low-percentage situation. I'd take some dummy loads of what you are now using with your current mandrel and release the bolt, allowing them to strip off the magazine. Eject them and take another "after" measurement. If your bullets are moving AT ALL, I'd make my next mandrel .002" smaller. If it is with brass you just sized - I'd go .003" smaller. Keeping the proper (adequate) tension without overdoing it can be a balancing act with necks that are hardening with use if not annealed as well. As they harden, they tend to "spring back" in diameter more - which gives you less tension. A good reason to anneal A/R brass after every fourth firing - and sooner is better.

 

[bgblue1978]

Searcher, I don't have a bushing die for this cartridge. I understand the methods for controlling next tension with a bushing or with a mandrel, my question was more if it's worth controlling or if the crimp was adequate. I guess the simple answer is if you're happy with the accuracy then leave it, if not get the right bushings/mandrels. I'm not a good enough shooter to have expectations of all of my ARs shooting legit sub .6" groups and definitely not WAY better, especially not off a harris bipod and homemade sock. But this gun in particular I do expect to shoot .5s or better with the right loads.

RKS: it's a 24" 6.5 twist target crown barrel. I don't think my issue is with the barrel or upper, it shoots factory ammo fine. I'm going to order a smaller mandrel and test. Mind sharing any of your loads? I will work up as always but I ask specifically because you have the same barrel presumably from the same reamer. I'm going to do some shooting off the rest next time, and I'll try some RL15 as well thanks.