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Discussion Starter · #1 ·
There have been a lot of questions about the Swedish Mauser actions (m/94,96,38) that have been converted to .30-06 and .270 caliber hunting rifles. This has been done in the past, in Sweden, primarily by Stiga, Vapen Depoten, and the Carl Gustaf factory. This conversion may also have been done by independent Swedish gunsmiths.

After reviewing my notebooks and corresponding with knowledgeable gunsmiths and gun dealers in Scandinavia, it appears that the main area of concern is in the modification of the feed ramp to extend the magazine length to fit cartridges other than the original 6.5x55.

If the feed ramp on the aforementioned models of Swedish Mauser is ground or machined down too much, it weakens the bottom of the receiver and particularly the support of the lug recess. This of course can lead to structural failure of the receiver if done improperly. Unfortunately, I do not know what the dimensional limits are for modification of the feed ramp. It should also be noted that extensive grinding of the feed ramp also negates the original heat treatment further weakening the metal. But, it is my understanding that some of these rifles were heat treated after modifications.

Anyone having one of these type of conversions should inspect the rifle carefully for any signs of imminent failure, i.e., cracks, or other indications that too much metal has been removed from the feed ramp.

Under CIP standards for the Swedish 6.5x55 cartridge, Pmax pressure is rated at 55,114 PSI (3800 bars) and SAAMI pressure max is at 51,000 PSI. This is for the cartridge. Firing higher pressure rated cartridges in Swedish Mausers that have had extensive feed ramp modifications just doesn't seem to me the thing to do. But, thousands of these rifles have been modified and converted to the .30-06 and .270 cartridges but I am not finding much documented data on the failure rate that these rifles may have. Anecdotally, there are a lot of stories about catastrophic or near catastrophic failures of such converted rifles, particularly Stiga conversions. But, without documentation they are just anecdotes.

So, if you have one of these conversions be careful. Have it inspected by someone who knows what to look for or has the appropriate detection technology for finding stress in metal.

Provisionally, I don't think this caution applies to the Husqvarna commercial m/94-38 actioned rifles converted to 9.3x62 since I do not believe the feed ramps were modified on these rifles.
 

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i had the kimber---308 and 6 x 55 never looked or thought to look in that area......very good thoughts to personally research KRIGG.
i do wonder if any signs from the subatomic stretching, the elasticity of the steel structure would show up as: a slight crack before the actualization of compeled failure?.
what do you think?
 

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Discussion Starter · #3 ·
Hi Daniel,

Personally, I've never seen a cracked one because until just recently it never occurred to me either to look in that area. What alerted me to the feed ramp situation was that a gunsmith friend of mine in Norway mentioned in passing a Stiga letting go because of the ramp modification. Most of the focus has been on whether the Swedish Mauser action was strong enough for .30-06 level pressures, but the whole picture gets changed when the receiver may have been weakened. Another acquaintance in Denmark who has seen a lot of Stiga and gunsmith modified rifles, refuses to do work on them because of liability issues. The next time I get a hold of a Stiga, I will definitely be looking at the feed ramp.
And remember, incipient fractures in the metal may not be visible to the eye and it might be worth while to get a receiver Magnafluxed or fluoroscoped to see if there are any cracks starting up.
 

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Same problem with 375 H&H length conversions on FN Model 98's.

I looked at my strengthened 38 (Model 649) in 9.3x62 in comparison to a 1904 date Model 94 military carbine in 6.5x55 and the feed ramp was widened a bit on the 9.3 and polished but no appreciable metal was removed from behind the lower lug seat. The H&H magnum conversions on the GEW98/K98k/FN 98's were questionable in the old days because of the metal removed behind the lower lug to allow a longer magazine box/cartridge. It usually worked but could really be an issue if someone reamed the chamber to accept Weatherby rounds. The original Weatherby's were built on FN actions however. I think the problem might show up as lug setback. Jack Lott (of .458 Lott fame) told of the upper lug cracking on the bolt of a .375 H&H FN commercial action of his. Probably due to lug setback (lower) until the upper lug was doing all the work.
 

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Discussion Starter · #6 ·
The lug setback you describe is said to be found frequently in the Stiga rifles. Again, that is anecdotal information and I don't have good data on that.
 

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And "strengthened" 38 recievers which have no thumslot cut are no stronger than any other action as far as breaching. All the breaching strength is in the forward reciever ring with the bolt lugs riding on the top and the bottom as is the concern of this feedramp mod thread.
 

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Modification of the magazine for the 9.3 round did not entail extending the magazine front forward and so the base of the feed ramp starts at the same point as in the original 6.5's. The ramp was widened a bit because the bullet tips are a bit farther apart as the bolt starts to push the rounds forward because of the little taper of the longer 9.3 round. It does not appear that very much actual metal was removed. If you want to peer into an action and get a scare- look at an Interams Mark X that was factory built in .375 H&H; they ground out a lot of metal from behind the lower lug, extended the magazine box, etc. I agree that the use of "strengthed" to describe the actions without a thumb cut is a misnomer. I agree with Baribal that lug setback is much perferable to fracturing and that is why Mauser made the cores soft. I wonder about the notches cut into the receiver ring (topside) to let .30 M2 rounds feed from a stripper clip in regular 8x57 length actions like Peruvian 1935's and others. The original Mauser plant made longer actions for longer cartridges and stretching the actions beyound the original design specifications is questionable. Kriggevar's caution is wisely heeded.
 

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The Kimber's suffered from setback more from excess headspacing than anything else. they were hastily cobbled together rifles meant to maximize profits and many were down right dangerous.

I worked on four or five Kimber sporters last year uin 6.5x55. They all had excess headspace. Seems barrels were simply reprofiled and screwed on. Several had the top lug contacting the breech face. Hard to check headsace under those conditions.

FN and Interarms made .375 H&H's, as well as Early Weatherby's built on FN actions, had much more of the bottom lug web (feed ramp to some) removed than an -06 conversion on a '96. Strength is a relative term, how is it being gaged? Gas handling is a much more valid reason to shy away from high pressure conversions on '96's. Then again, compare gas handing of the 96 to a pre-64 Winchester Model 70.
 

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What is the SAAMI and CIP PSI for the .270Winchester ctg.?

My VitV loading manual gives CUP, CIP and European PSI measurements for many ctgs. All are very similar in number - ie: CUP, CIP and "their" PSI are very similar - almost identical numbers - ie: a round might show 55,000CUP, 55,100CIP and 55,100PSI as listed in their manual. For those same rounds loaded in the States, the PSI numbers are considerably higher, ie: 55,000CUP is actually 63,400PSI, not 55,100PSI as given - different method of measuring PSI? - One would think PSI is PSI - an absolute measure ie: pounds per square inch. One country's pound per square inch cannot or should not be different than another's pound per square inch - sthe relative POUND has more or less ounces in it - or perhaps the ounce weighs differently - or their inches are larger or smaller - which isn't the case, I'm sure. So- why are they different and since they are different - their CIP PSI's have no meaning here, where we've come to understand the US system which is being used in US loading manuals more and more.

All '06 based rounds, that includes the .30/06, .270, .280, .35 Whelen - including the wildcats on standard shaped (base and shoulder) brass, .338/06 for instance, can all be loaded normally, to the highest listed peak pressure for that case, which appears to be the .270. This means that any handloader who has an inkling of what he is doing, can load his '06 or Whelen (or whatever '06 based round) to .270 levels - in appropriate actions, which is exactly what was done with the .338/06, now a proprietry/ie: factory round. I do not consider the various small ring'd 96's, 94's etc to be appropriate actions.

Since Hodgdon data goes to a maximum listing of 64,000PSI in the .270 loading manual data, I assume 64,000 or perhaps 100 or 200 PSI more is the SAAMI max. What's the CIP max? I am most assuredly NOT suggesting anyone increase their loads.

However, my 6.5x55 gave slightly less than identical pressure, by an accurate measure, to Norma factory loads, and was able to push 129gr. Hornady's to 2,960fps from it's brand new, previously unfired, 22" bl. I am assuming that firing the factory 156gr. bullets 'slightly' hardened the brass that was then used in developing my handloads. All measurements were made in once fired brass only. I then used other brass, which had higher case capacity than the Norma, and loaded to those same meaurements, which gave the same relative velcoities.

A .270 Winchester has no real advantage over the original 6.5x55 round - my suggestion is NOT to fix something that isn't broken. I would certainly NOT fire a .270 or .30/06 round in those listed actions.
Daryl
 

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Adding to the confusion of CUP vice PSI, in the days before peizo-electric transducers to measure chamber pressure in psi, CUP measurements were often listed as "PSI" even though the measurement was taken by measuring a copper crusher and using a chart of approximated PSI. CUP was a relative measure and a computational estimate of PSI through the distortion of the copper pellet, not an absolute measure of PSI.
Then there are the differences in transducer placement vice copper pellet placement on the chamber, but this is really taking us OT. There are plenty of authoritarian references that one can read on the subject.
 

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Adding to the confusion of CUP vice PSI, in the days before peizo-electric transducers to measure chamber pressure in psi, CUP measurements were often listed as "PSI" even though the measurement was taken by measuring a copper crusher and using a chart of approximated PSI. CUP was a relative measure and a computational estimate of PSI through the distortion of the copper pellet, not an absolute measure of PSI.
Then there are the differences in transducer placement vice copper pellet placement on the chamber, but this is really taking us OT. There are plenty of authoritarian references that one can read on the subject.

Your "How many psi in a CUP? Well, just read an article, can't remember where - handloader, rifle, DG Journal - ???- that now there is a formula for that conversion that takes into consideration case capacity/bore size ratios or some such. It would need those ratios in order to work, but even then would only be roughly approximate, I would think.

Ackley's books are a prime example of calling CUP, PSI in the 'old days'. We are beyond that now, I would hope. Hodgdon seems to have the best data or at least some of the best data. Of interest, is where they list both CUP and PSI in the same loading data. It is easily cross-referenced to see the approximate similarities in some rounds, especially the straight ones or gross differences in the huge case but small bore rounds.

Still - the situation is a 64,000PSI Factory round in a Model 96 - look no further than the .270 Winchester.
 

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AMMOe has the correlation of CUP and PSI correct; there is no direct, predictable, or practicable correllation. Many guess at it because they've seen a load or round that generates say 50K CUP and 60K PSI and assume a correlation there. But it isn't what it appears, it's just coincidental. 308/7.62 NATO and 30-06 chamber pressures being measured in CUP and PSI are the two most mistunderstood by both the general public and otherwise quite knowledgeable gun nuts. CUP is all theoretical computation based on compostion of a maleable "standardazed" copper pellet that gives a calculated peak pressure, duration of the peak and whether or not the peak dwell was long enough to act in crushing or only part of the pressure curve actively crushed the pellet is actually unknow with this method. Piezoelectric transducers are much more accurate and repeatable as well as giving a trace for a pressure curve (we used paper strip charts in the old days, computers now). They are, however, not even put in the same point of the chamber as copper pellets were, hence even less direct correlation.
So if you see a load at 50k CUP "PSI" for 30-06 or 308 Win, it is not safe to assume that is true PSI. For safety, one must assume that these CUP pressures correlate to the SAAMI working pressures of 60K and 62K piezo-electric measured PSI respectively.
**But again, There is no mathematical formula that will convert CUP to PSI!
 

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AMMOe has the correlation of CUP and PSI correct; there is no direct, predictable, or practicable correllation. Many guess at it because they've seen a load or round that generates say 50K CUP and 60K PSI and assume a correlation there. But it isn't what it appears, it's just coincidental. 308/7.62 NATO and 30-06 chamber pressures being measured in CUP and PSI are the two most mistunderstood by both the general public and otherwise quite knowledgeable gun nuts. CUP is all theoretical computation based on compostion of a maleable "standardazed" copper pellet that gives a calculated peak pressure, duration of the peak and whether or not the peak dwell was long enough to act in crushing or only part of the pressure curve actively crushed the pellet is actually unknow with this method. Piezoelectric transducers are much more accurate and repeatable as well as giving a trace for a pressure curve (we used paper strip charts in the old days, computers now). They are, however, not even put in the same point of the chamber as copper pellets were, hence even less direct correlation.
So if you see a load at 50k CUP "PSI" for 30-06 or 308 Win, it is not safe to assume that is true PSI. For safety, one must assume that these CUP pressures correlate to the SAAMI working pressures of 60K and 62K piezo-electric measured PSI respectively.
**But again, There is no mathematical formula that will convert CUP to PSI!
Everyone knows there is no direct correlation between CUP and PSi. I was pointing out that he stated the 30-06 and 270 operated at 50, 000 PSI. That is not the case.
 

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Up until now, we all knew that there is no direct relationship or co-relationship or mathematical formula that would convert one to the other CUP to PSI or PSI to CUP.

What I related about the article is correct, not BS or thoery of mine - I merely wrote what I'd read - the ariticle, much too mathematical and complicated for me, showed and proved that there is an actual formula that works. I'm now thinking it might have been in the DG and SS Journal - or Rifle or maybe Handloader.

Whether this is accepted or not by those much more knowledgable than ANYONE here remains open, there has not been a definitive ruling - simply repeating 'a rule or knowledge' declared 20 years ago, lacks accuracy in this case just as it would be in medicine - until this formulation is checked out by better mathematitions and ballisticians.
 

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Discussion Starter · #19 ·
In 2002 a fellow by the name of Denton Bramwell published in Varmint Hunter magazine an article where he presented a regression analysis of CUP and PSI measurements where he used ANSI/SAAMI pressure measurements of CUP and PSI values and found a high correlation coefficent between the two measures for a set of selected cartridges. He also noted that this correlation seems to be reliable within a range of pressures and that the reliability of the correlation drops off at values below 30,000 PSI. Here is the link to that article: http://www.shootingsoftware.com/tech.htm I agree with z1r that the pressure aspect of the discussion as been pounded on enough. I was hoping to get some photos and at least some anecdotal information about the modifications made to the .270 and .30-06 chambered small ring Mausers by various Swedish companies and gunsmiths.
 
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