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Need help with bolt weight math 22lr
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  gun410999

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Posted: March 04 2017 at 10:14pm | IP Logged Quote gun410999

And for the firing pin should I do anything or shape the end of the 1/16" firing pin? I see some online that are shaped like flat head screw drivers or just shaped to a cone/Spear shape on the end. And how far out should it pertrude from the bolt face?
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  backbencher

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Posted: March 05 2017 at 10:01am | IP Logged Quote backbencher

gun, you are overthinking this.  Ruger 10/22s shoot Stingers, hypervelocity .22" LR, and everything else w/ a .4 lb bolt.

If you're wanting to suppress it and want the ultimate in quiet, then use a heavier bolt; if it doesn't cycle w/ the light stuff like you want it to, drill holes in it to reduce weight or cut some length off the tail.

Don't worry about the shape - leave it a little long - you can always cut it short or change the shape if you're not getting ignition or you're piercing the rim.
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  gun410999

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Posted: March 05 2017 at 11:06am | IP Logged Quote gun410999

backbencher wrote:
gun, you are overthinking this.  Ruger 10/22s shoot Stingers, hypervelocity .22" LR, and everything else w/ a .4 lb bolt.<br><br>If you're wanting to suppress it and want the ultimate in quiet, then use a heavier bolt; if it doesn't cycle w/ the light stuff like you want it to, drill holes in it to reduce weight or cut some length off the tail.<br><br>Don't worry about the shape - leave it a little long - you can always cut it short or change the shape if you're not getting ignition or you're piercing the rim.<br>

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Ok I'll probably go 4" long .5 pound bolt. I'm probably not gonna suppress it. And then my last question(or atleast I think it is) so I got this Spring and I'm wondering how much rooom in the receiver should I give it?
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  ds1948

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Posted: May 21 2017 at 5:22pm | IP Logged Quote ds1948

I always love reading up on formulas used to estimate bolt weight for various firearms. As this is a passion of mine, I did a write up earlier this year on the same topic.
http://www.weaponeer.net/forum/forum_posts.asp?TID=25363&KW= blowback+rifle

On top of this, Chinn used the following formula for bolt weight calculations.

(wb)*dv=(wp/7000+wg/14000)*dv. wb is the weight of the bolt in pounds. the dv next to it is the delta bolt velocity (10 to 12 ft/s in most actions).wp is the weight of the projectile in grs. followed by wg which is the powder charge in grs. the last dv is the delta velocity of the projectile. a conversion of .69*by the projectile velocity works well for most rounds. Once you plug in 40gr. bullet, 2 gr. of powder, a velocity of 1200fps, and assume a bolt velocity of 12 you get a weight of .42 pounds. Play around with this for rounds such as the 9mm and the .45 acp. It works pretty well. For bottleneck cases you merely take the bolt head area/bullet area. Bolt head is always the internal area of the rear of the case in pressure calculations. In straight walled cases this is the bullet diameter but in bottlenecked cases this is not the case. I hope I didnt deviate the thread any but I love the idea of blowback weapons and hope to build a blowback .223 oneday.
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  backbencher

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Posted: May 22 2017 at 6:52pm | IP Logged Quote backbencher

http://www.weaponeer.net/forum/forum_posts.asp?TID=25363

That would be a heavy gun - but tolerable in a tripod or pintle mounted weapon, like in a motorcycle sidecar.
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