Forums
New posts
Search forums
What's new
Articles
Latest reviews
Author list
Classifieds
Log in
Register
What's new
Search
Search
Search titles and first posts only
Search titles only
By:
New posts
Search forums
Menu
Log in
Register
Install the app
Install
Forums
Rifles, Reloading, Optics, Equipment
Reloading
Help! Extreme spread and standard deviation loads
JavaScript is disabled. For a better experience, please enable JavaScript in your browser before proceeding.
You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an
alternative browser
.
Reply to thread
Message
<blockquote data-quote="Bart B" data-source="post: 492363" data-attributes="member: 5302"><p>In my many years of highpower competitive shooting, I've talked with lots of national champions, record setters and such folks who shoot the most accurate box magazine rifles in the world. Some of them have rifles and ammo that put benchrest rifles to shame aas far as accuracy's concerned.</p><p></p><p>Two things that usually cause high muzzle velocity spreads; primers and firing pin springs. </p><p></p><p>If the firing pin spring is too weak, it won't smack the primer hard enough to make its compound detonate (burn really, really fast) with the same repeatable amount of heat. Firing pin springs do weaken over time, even when they're uncocked in the rifle. Replace them every two or three years. And using a stronger one that what is factory specs is usually a good idea for uniform primer performance. As these springs weaken and primers are no longer popping uniformly, the powder charge won't burn consistantly. Velocity spread increases and average muzzle velocity for a given barrel and powder lot and charge weight goes down.</p><p></p><p>A couple of folks have tested large rifle primers in modified .17 Rem cases with a BB seated but no powder used. Shooting the BB's through a chronograph and using the velocity average is the indicator. Primers with the lowest average velocity produced the lowest muzzle velocity spreads and best accuracy when shooting bullets. Magnum primers were the worst. Which is probably why I got best SD and accuracy with the mildest large rifle primer with my 30 caliber magnums as well as .308 Win. ammo. RWS 5341 primers....expensive, but they really did do wonders. Wolf large rifle primers are popular these days with those shooting the best scores.</p><p></p><p>Exact powder charge weight's not all it's cranked up to be. When a bunch of us did some testing for a many-hundred thousand round batch of .308 Win. match ammo using new Winchester cases, Fed. 210M primers and metered IMR4895 (3/10ths grain spread), mild lots of primers produced sub 3-inch test groups at 600 yards. Not too shabby in my opinioin. Note that benchresters typically meter their charges instead of weighing them for matches up to 300 yards.</p><p></p><p>Ones technique in testing ammo shooting their rifle as it rests atop somthing on a bench may well impact their muzzle velocity readings. I've seen a few people get near 100 fps spread in average velocity shooting the same rifle and ammo. It's all in how hard they held the .308 Win. against their shoulder.</p></blockquote><p></p>
[QUOTE="Bart B, post: 492363, member: 5302"] In my many years of highpower competitive shooting, I've talked with lots of national champions, record setters and such folks who shoot the most accurate box magazine rifles in the world. Some of them have rifles and ammo that put benchrest rifles to shame aas far as accuracy's concerned. Two things that usually cause high muzzle velocity spreads; primers and firing pin springs. If the firing pin spring is too weak, it won't smack the primer hard enough to make its compound detonate (burn really, really fast) with the same repeatable amount of heat. Firing pin springs do weaken over time, even when they're uncocked in the rifle. Replace them every two or three years. And using a stronger one that what is factory specs is usually a good idea for uniform primer performance. As these springs weaken and primers are no longer popping uniformly, the powder charge won't burn consistantly. Velocity spread increases and average muzzle velocity for a given barrel and powder lot and charge weight goes down. A couple of folks have tested large rifle primers in modified .17 Rem cases with a BB seated but no powder used. Shooting the BB's through a chronograph and using the velocity average is the indicator. Primers with the lowest average velocity produced the lowest muzzle velocity spreads and best accuracy when shooting bullets. Magnum primers were the worst. Which is probably why I got best SD and accuracy with the mildest large rifle primer with my 30 caliber magnums as well as .308 Win. ammo. RWS 5341 primers....expensive, but they really did do wonders. Wolf large rifle primers are popular these days with those shooting the best scores. Exact powder charge weight's not all it's cranked up to be. When a bunch of us did some testing for a many-hundred thousand round batch of .308 Win. match ammo using new Winchester cases, Fed. 210M primers and metered IMR4895 (3/10ths grain spread), mild lots of primers produced sub 3-inch test groups at 600 yards. Not too shabby in my opinioin. Note that benchresters typically meter their charges instead of weighing them for matches up to 300 yards. Ones technique in testing ammo shooting their rifle as it rests atop somthing on a bench may well impact their muzzle velocity readings. I've seen a few people get near 100 fps spread in average velocity shooting the same rifle and ammo. It's all in how hard they held the .308 Win. against their shoulder. [/QUOTE]
Insert quotes…
Verification
Post reply
Forums
Rifles, Reloading, Optics, Equipment
Reloading
Help! Extreme spread and standard deviation loads
Top