(HL) Guess what day it is... Guess what DAY IT IS... Handloading Hump-day! Today, well address Mr. Timothy D. Ehrhards questions about crimp and case-neck tension for accurate rapid-fire ammo used in Service Rifle competition, plus our Handloading of highly-accurate pistol competition ammo. But first, a word about this weeks photos. The first is an old file photo of one of our better 20-shot groups at 600 yds, testing ammo from a machine rest (200-18X). Looking closely, one can see a pic of the Machine Rest. Our second pic shows an old 600 yard National Record fired at 600 yards by one of our shooters using a sling and iron sights with the same handloads -- 200-16X! As you can see, our rifleman didnt give up much to the machine rest! And now, to our tips! CRIMP of match-grade rifle ammunition. First, bear in mind that introducing a crimp to your match ammo adds a new possibility for inconsistency, both round-to-round and lot-to-lot. (Youll notice very few high quality match bullets have crimp cannelures, which distort the bullet jacket.) And, for accuracy, consistency is the name of the game! We dont crimp our match rifle ammunition, but with that goes a caveat or 2. Our long range ammo (600 yards and beyond) is almost always intended for single-loading into the chamber, unless made for an Action Shooting or Sniper event. Using virgin brass and sizing dies with interchangeable neck bushings that let us control neck diameter to 0.001, we ensure adequate, but not excessive neck tension. Generally, that means setting case neck diameter about 0.003 smaller than it will be once the bullet has been seated. This dimension can vary some, depending on several factors. As to ammo that will be used for rapid-fire, very long experience with M1s, M14s and M16s has shown that standard-type die sets with a fixed neck and expander ball very rarely, if ever, allow bullets to be set back into the case upon cycling. Rapid-fire ammo loaded with bushing-type dies should be tested in practice to ensure adequate neck tension before competition use. Be aware that case necks tend to work-harden with repeated reloading. This can change neck tension from what it was when using new or once-fired brass, unless cases are annealed periodically. This is another good reason to segregate case lots by number of times fired, to ensure consistent neck tension within lots. PISTOL AMMO: yes, we do develop our own match pistol ammo. We tailor it to the various bbl-manufactures and chamber types used in each new cohort of match pistols. While there are many combinations of powder, primer, bullet and case that can potentially give winning accuracy, we do find one aspect that is often overlooked. Taper-crimp of 9mm and .45 ACP match ammo, in particular, can be an important contributor to accuracy. Once we have promising combinations identified, we will test samples (10-20 rds each) with crimp varying in 0.001 increments. Often, this will be a deciding factor on which combination we will adopt, and results can be dramatic. To measure crimp accurately, place the jaws of an accurate dial caliper reading to 0.001 or finer EXACTLY at the case mouths edge. Take several readings around the circumference of the cartridge case mouth to control for slight variances in case wall thickness. Measure several rounds to ensure you have accurate dimensions. Once again, it pays to segregate cases by headstamp and number of times fired, if possible. We hope this edition of Handloading Hump-day has been helpful, and keep those comments and questions coming! Happy Holidays to all, and stay safe!
Posted on: Wed, 17 Dec 2014 15:35:08 +0000
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