Long Range Hunting Online Magazine


Go Back   Long Range Hunting Online Magazine > Rifles, Reloading, Optics, Equipment > Gunsmithing


Reply

FN action: BOLT THRUST REDUCTION

 
LinkBack Thread Tools Display Modes
  #8  
Old 05-12-2011, 03:28 PM
SPONSOR
 
Join Date: Mar 2010
Location: on the Southern Plains
Posts: 1,123
Re: FN action: BOLT THRUST REDUCTION

Out of an Oberndorf 1935 Peruvian chambered in .30-06 A.I. Owner allowed "he can get .300 Win. Mag. velocities with his handloads". Cost him partial vision loss in his right eye and a nice rifle!
Attached Thumbnails - Click to View Larger
FN action: BOLT THRUST REDUCTION-bolt-001.jpg   FN action: BOLT THRUST REDUCTION-bolt-003.jpg  

__________________
"Shoots real good!": definition; it didn't blow-up in my face. Not everything can be fixed on an internet forum!
Reply With Quote
  #9  
Old 05-12-2011, 03:57 PM
Bronze Member
 
Join Date: Dec 2010
Location: Arizona
Posts: 32
Re: FN action: BOLT THRUST REDUCTION

Hello Short Grass I appreciate your response. The reason I posted this thread is attempt to quantify how much If any I can gain by going to an A.I. chamber. I am in no way shape or form interested in damaging my rifle/me. I just thought I might be able to reduce or keep the B. T. the same and pic up a few FPS. I was planning on using the max published 96 swede loads in a couple of my loading books. I may be a bit premature with posting this here as I dont even have it stocked yet. Any thoughts or input are appreciated thanks again..... George
Reply With Quote
  #10  
Old 05-12-2011, 05:35 PM
Silver Member
 
Join Date: Jul 2009
Location: Salmon, Idaho
Posts: 392
Re: FN action: BOLT THRUST REDUCTION

Quote:
Originally Posted by shortgrass View Post
The 'rules', as you call them, are there so folks don't hurt themselves. I realize published data is what it is out of respect for the '94/'96 Swedish Mausers. If you read the intro in the loading manuels, it says in an action more modern then the Swedish Mausers, more velocity w/stouter loads is possible. Modern made actions and brass make it possible. By Ackley-izing the 6.5 x 55 you may gain 150fps or so. If you need more, you might look at a different cartridge case. Your desired 3100fps. is a max load for the .264 Win. Mag., which a much larger volume. There have been 100s of thousands of Mauser '98s converted to feed and fire the Winchester Magnums, I happen to have a few of my own. Some, like your FN, came from the factory for the Win. Mags. So,to me, there's no question as to their strength. I have seen more than one, over the years (the last 35 or so) that have set back the locking lug abutments, turning an otherwise fine action to junk. To reach that 3100fps velocity in a case smaller than that the size of a Win.Mag. will drastically increase pressures and I don't think the straight walls of an Ackley case will be enough help in the Mauser. But, before I did it to a 6.5x55, I'd step up to a case with more capacity to try to keep pressures under control. And, by the way, that 2800 to 2850fps. seems to be the velocity range the guys shooting .260's, 6.5x47's and 6.5-284's in competition are at for their best accuracy. You might send it like Captain Kirks' 'phaser' but does it go there accurately? All of this has been tried 20, 30, 40 years ago. If you look around some of the gunsmithing books and on the web I'm sure you can find some pics of catastrophic failures. Floor plates blown out/off & mag boxes swelled, stocks splintered, bolts unremovable from the action because of set back. A well made '98 is a fine action, but not the one I'd want to try to 'hot rod' beyond its capabilities or past the strength of modern made brass cartridge cases.
FYI, nobody "desired" 3100fps, I just stated that it might be attainable or approachable with the Ackleyized Swede. BTW I'm getting 2850 with 45.5grns of H4831, Lapua brass, Fed primers, and Hornady 140g SST from a 26" barrel, that is 1.5 grains<the published max load for this powder in Nosler #6 Manual. Hardly what I would call "hot rodding". Their test barrel was 23" and gave 2663fps with 45.0g, oh and yes it goes there accurately-3/8"@100yards. I'm not advocating that we all "hot rod" our rifles, but this example illustrates how different two rifles can be. By all means, practice safe reloading techniques, always approach max charge weights with caution, know how to recognize pressure signs, but on the same token know your cartridge/action history too and realize that factory ammo and reload data may not reflect actual cartridge potential and just because it's the newest uber magnum doesn't mean it's better. Funny that you mentioned the host of new 6.5/.264 cartridges, I'd say this was all done well over 100 years ago and that Rem and Lapua have reinvented the wheel. If these velocities (2800-2850) are safe in .260 (53g H2O) and 6.5x47L (49g H2O), why would they not be safe in the same action chambered for the larger volume 6.5x55 Swede (58g H2O)? I don't know how many grains of H2O you gain by going to the BJAI but it stands to reason that any gain would increase volume and thereby cartridge potential and in concert with the reduced bolt thrust, well sounds like a win win situation to me. Those darn Swedes were on to something and so was Ackley. Don't know if you've noticed but the Swede has a lot of body taper a common trait in military cartridges, but by blowing most of the taper out of the body of the case more pressure is exerted against the walls of the chamber and less rearwards into the bolt face reducing bolt thrust. This is because as pressure is exerted outwards against the walls of the case the tapered walls of the chamber act like a wedge redirecting forces and squeezing the case rearward into the bolt face. Less taper equals less bolt thrust. This and moving the shoulder forward and out to 40 degrees increases case volume. How much, I don't know, can't find it published anywhere. Is it enough to get to the next accuracy node beyond 2850fps? I don't know, I don't own one, wish I did. Just sayin. Sorry for hijacking your thread Bigstrap.
Reply With Quote
  #11  
Old 05-12-2011, 09:39 PM
Platinum Member
 
Join Date: Jun 2004
Location: Texas
Posts: 1,027
Re: FN action: BOLT THRUST REDUCTION

Ted, thanks for the "dirty pictures". One of the many things I like about the Mauser large ring actions is the 3rd "safety" lug. I'm guessing the action survived, but it looks like the bolt set back far enough to engage the safety lug. Also, the case must have ruptured badly enough for all kinds of crap to get in his face. I'm a little surprised the gas vents and shroud didn't catch or divert it. Can you share any more details? Did the floorplate blow open (or off)? If he had rounds in the magazine, did any of them go off?

I was also wondering if maybe the stock blew apart and caused the injuries.

A while back a friend wanted me to barrel up a Mexican small ring Mauser for him in 6.5 x .284. I just couldn't make myself do it. It might have been alright, but I balked. I did it for him on a F N commercial large ring with no hesitation. A 6.5 x 55 or an improved version should be a cake walk for that action.

Good thread.

Tom
__________________
Texas State Rifle Association Life Member
NRA Endowment Life Member

A big fast bullet will beat a little fast bullet every time

Last edited by specweldtom; 05-12-2011 at 09:44 PM. Reason: add question about rounds in the magazine
Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes


Similar Threads for: FN action: BOLT THRUST REDUCTION
Thread Thread Starter Forum Replies Last Post
Break action vs. Rolling/Falling Block, vs. Bolt action Dgutter Rifles, Bullets, Barrels and Ballistics 6 03-11-2011 11:15 AM
Pressures, Case Strength and Back Thrust ADMIN Technical Articles - Discussion 5 02-13-2011 12:12 PM
savage short action bolt head vrs long action foreign The Basics, Starting Out 4 07-02-2010 11:42 AM
Bolt thrust and case taper? jcoop Long Range Hunting & Shooting 3 11-21-2009 10:58 PM
Wanted REAL BAD Remington short action Bolt with a 308 bolt face Darryl Cassel Guns For Sale 4 07-23-2002 04:24 PM

Current Poll
Do you archery hunt for elk?
YES - 31.35%
58 Votes
NO - 52.97%
98 Votes
Not yet, but I plan to. - 15.68%
29 Votes
Total Votes: 185
You may not vote on this poll.

All times are GMT -5. The time now is 12:45 PM.


Powered by vBulletin ©2000 - 2014, Jelsoft Enterprises Ltd.
Content Management Powered by vBadvanced CMPS
All content ©2010-2014 Long Range Hunting, LLC