Page Index Toggle Pages: 1 Send TopicPrint
Normal Topic BSA MK II strength (Read 944 times)
Dales
Senior Forum Member
****
Offline



Posts: 272
Location: Western NY
Joined: Oct 21st, 2013
BSA MK II strength
May 29th, 2019 at 1:17pm
Print Post  
I found a BSA MK II on Gunbroker That was converted to center fire and chambered to 6PPC. Are these actions strong enough for this ?

Dales
  
Back to top
 
IP Logged
 
oldman46
Full Member
***
Offline



Posts: 191
Joined: Sep 21st, 2016
Re: BSA MK II strength
Reply #1 - May 30th, 2019 at 12:14am
Print Post  
Is the BSA MKII one of the international series of 22rf target rifles?. I've heard of doing a 22 hornet conversion but nothing other than that. PPC can run some high pressures as I remember and benchrest shooters in some cases were pushing the envelope. So in answer to your question I would have some serious doubts about this rifle and it's chambering. Probably has a benchrest style chamber, which means the cases have to be weighed, sorted by weight,case necks would have to be turned to fit the chamber and other considerations. Does any data come with the rifle regarding chamber neck diameter and twist?. If not then don't waste your time and money on this firearm. Frank
  
Back to top
 
IP Logged
 
ratseye
Full Member
***
Offline



Posts: 128
Location: Eastern, PA
Joined: Feb 28th, 2017
Re: BSA MK II strength
Reply #2 - May 30th, 2019 at 7:46am
Print Post  
The Mark II has a pretty heavy side wall and quite strong but was originally chambered for the 22 LR. The problem is the 22 LR Pmax is around 24,000 PSI from SAMMI and the 6mm PPC is rated at a little over 58,000 or more than double. The second problem is case head diameter and the PPC is roughly three times the 22 in area. This is really important because it is the back thrust that does the damage. Do the math and load wisely. ratseye
  
Back to top
 
IP Logged
 
Remington40x
Full Member
***
Offline



Posts: 161
Location: Bucks County, PA
Joined: Oct 18th, 2007
Re: BSA MK II strength
Reply #3 - May 30th, 2019 at 12:10pm
Print Post  
The issue with the 6mm PPC in a small frame Martini is probably not case head thrust on the breech block, but the thickness of the barrel walls at the threads.  Bob Snapp used to warn against using high pressure cartridges with a diameter greater than the .222 family because the chambers could swell at the threads, ruining the barrel and making extraction difficult or impossible.  Cartridges in the .30-30 family were acceptable, as their operating pressures were much lower.

I have two .225 Winchesters built on Model 12/15 actions and had discussed that particular cartridge with him in some detail.  He recommended limiting pressures to starter loads or slightly hotter, but not hot-rodding the cartridge, which some people did.  I don't know if there is any more meat in the threaded section of a Mark II than there is in a 12/15, but someone who owns both could measure and let us know.
  
Back to top
YIMAIM  
IP Logged
 
ratseye
Full Member
***
Offline



Posts: 128
Location: Eastern, PA
Joined: Feb 28th, 2017
Re: BSA MK II strength
Reply #4 - May 30th, 2019 at 2:06pm
Print Post  
I read that about the little Martini and have had several that had been converted to various 30-30 case configurations. The most current is a BSA Mark 12 in both 22 and 357 Herrett. After reading your post, I measured the barrels out of curiosity and the root of the thread measures .665" on both. I measured the ID of the Herrett at the same point and got .412". That yields a chamber wall of about .253" at that point. The barrel diameter at the point where it meets the receiver is .890" on the Herrett barrel and .998" on the 22 LR barrel. The receiver is 1.2" wide where the barrel threads in and the sides of the receiver going back are .229" thick. This is a Model 12 take-down and not a Mark II. ratseye
  
Back to top
 
IP Logged
 
chipmaker
Full Member
***
Offline



Posts: 155
Location: san diego
Joined: Sep 24th, 2007
Re: BSA MK II strength
Reply #5 - May 30th, 2019 at 3:48pm
Print Post  
The barrel tendon of the Cadet Martini's is nominally 3/4 X 14 TPI and the BSA International M-1&2  is 3/4 X16 TPI, so they are essentially the same.
The 30-30 case base is listed as about .420" and the 6mm base is listed at .441".
In the example above, the difference in diameter between the tendon root and case wall was .253" which would give a wall thickness of .1265".
Bob Snapp advised against high pressure cartridges with cases 30-30 sized or bigger, in the Cadet sized Martini's, so I suspect that he would advise against the 6 mm PPC.
There is a report from Australia, on the difficulty in blowing up a Cadet, using a markedly overloaded 303 Br, suggesting that the little actions are quite strong.
Otto
  
Back to top
 
IP Logged
 
ratseye
Full Member
***
Offline



Posts: 128
Location: Eastern, PA
Joined: Feb 28th, 2017
Re: BSA MK II strength
Reply #6 - May 30th, 2019 at 5:04pm
Print Post  
chipmaker, you are correct and apologies to everyone because my math wasn't correct. I forgot to half the difference of course. Thanks for catching that error. ratseye
  
Back to top
 
IP Logged
 
Nevadaed
Newbie
*
Offline



Posts: 2
Joined: May 7th, 2016
Re: BSA MK II strength
Reply #7 - Nov 16th, 2019 at 12:33am
Print Post  
Iíve been shooting a customized cadet in .219 Donaldson Wasp since 1964.
  
Back to top
 
IP Logged
 
Page Index Toggle Pages: 1
Send TopicPrint