Mauser 96 Overpressure

[Clint08]

Joined the group so I could see if anyone has any ideas on this or possible causes. Bought a Mauser 96 a few weeks back at a gun show and still waiting for a field gauge to arrive so head space hasn’t been verified. Below is the relevant information.

Mauser 96 6.5x55 with original barrel
140gr Accubond
COL: 3.130 (Impossible to seat the bullet far enough to contact the lands)
Charge: 48.0grs N-165
Primer: CCI200
Brass: Norma (Never fired and only neck sized with OAL measured before loading)

1st Shot: 2708fps (No overpressure observed)
2nd Shot: 2855fps (Possibly slight flattening of the primer)
3rd Shot: 2929fps (Took extensive pressure to open the bolt, blown primer, and headstamp imprinted on the bolt)

Third fired case measured .010 over the unfired case when measured at the head. Shoulder had also moved forward .010. I loaded a total of 5 rounds for velocity testing and every charge was weighed. The remaining two cartridges I pulled the bullets and the charge was 48.0, as expected. The maximum charge from Hornady is 48.6grs and from VIHT is right at 50grs. My COL was greater than both sources by over .020. Also, both sources I’m assuming cap their listed pressures around 52,000PSI with Hornady even using the Mauser 96 as their test rifle. I can’t think of a reason for this massive over pressure, which I’m also assuming exceeded 70,000PSI given the velocity achieved and blown primer. I did take a bore brush and ammonia solvent to the bore before firing but I do not have a bore scope to distinguish excess fouling that may still be present. Any advice would be greatly appreciated.

 

[mac86951]

Wow! Glad you stopped! I've heard the 96 actions are less pressure than the later case hardened models.

Question, bolt lug set-back? Await the gauges and you'll have a better idea. You may (absolutely may) want to take that barreled action to a qualified Smith for a check-out. Hardness being my first question.

-Mac

 

[DGP4]

Maximum velocities for the 6.5X55 are in the 2700 fps range for 140 grain bullets. You are lucky you didn't get a face full of gas! I don't know the loading specs for the powder you mention, but I HIGHLY doubt they recommend loading to 2900 feet per second. I suggest you get a good loading data book and stick to the maximum loads shown therein.

 

[LCazador]

Joined the group so I could see if anyone has any ideas on this or possible causes. Bought a Mauser 96 a few weeks back at a gun show and still waiting for a field gauge to arrive so head space hasn’t been verified. Below is the relevant information.

Mauser 96 6.5x55 with original barrel
140gr Accubond
COL: 3.130 (Impossible to seat the bullet far enough to contact the lands)
Charge: 48.0grs N-165
Primer: CCI200
Brass: Norma (Never fired and only neck sized with OAL measured before loading)

1st Shot: 2708fps (No overpressure observed)
2nd Shot: 2855fps (Possibly slight flattening of the primer)
3rd Shot: 2929fps (Took extensive pressure to open the bolt, blown primer, and headstamp imprinted on the bolt)

Third fired case measured .010 over the unfired case when measured at the head. Shoulder had also moved forward .010. I loaded a total of 5 rounds for velocity testing and every charge was weighed. The remaining two cartridges I pulled the bullets and the charge was 48.0, as expected. The maximum charge from Hornady is 48.6grs and from VIHT is right at 50grs. My COL was greater than both sources by over .020. Also, both sources I’m assuming cap their listed pressures around 52,000PSI with Hornady even using the Mauser 96 as their test rifle. I can’t think of a reason for this massive over pressure, which I’m also assuming exceeded 70,000PSI given the velocity achieved and blown primer. I did take a bore brush and ammonia solvent to the bore before firing but I do not have a bore scope to distinguish excess fouling that may still be present. Any advice would be greatly appreciated.

Where did you find load and why did you start with such a stout load for fireforming brass?Always start with a moderate load for fireform then you can start your load work. Most new brass will have several thousands of excess headspace so it will fit in most rifles. Starting off with a heavy load while moving brass to fit your chamber size is not a good idea. You should be around 2700 fps with that bullet weight. That first load may have been in a cold chamber and once it gets hot things change quickly. Go back and start over with a fireform load. Maybe 44 grains but consult your loading manual.

 

[NV_Dmax]

That's a lot more powder than I can run in my Swede. 41gn H4831sc with a 140 Berger hybrid is my go to load. Looks like the Viht. is a bit slower. I would inspect the bore with a scope before going any further.

 

[jsn]

Rough throat, slow powder, possible SEE progression?

 

[Clint08]

Wow! Glad you stopped! I've heard the 96 actions are less pressure than the later case hardened models.

Question, bolt lug set-back? Await the gauges and you'll have a better idea. You may (absolutely may) want to take that barreled action to a qualified Smith for a check-out. Hardness being my first question.

-Mac

I’ve only ordered the field gauge as from what I’ve read SAMMI spec gauges are irrelevant for the military Mausers due to SAMMI not existing during that time frame. My concern is lug setback as you mentioned and I was able to reach out to a local gunsmith who said he can check it out for relatively cheap and also look at the throat and bore with a scope.

 

[mac86951]

I’ve only ordered the field gauge as from what I’ve read SAMMI spec gauges are irrelevant for the military Mausers due to SAMMI not existing during that time frame. My concern is lug setback as you mentioned and I was able to reach out to a local gunsmith who said he can check it out for relatively cheap and also look at the throat and bore with a scope.

Great idea; and agreed that SAAMI didn't exist, all that means is that it'll close on a no-go or not. Obviously a go gauge is good, no need there. No-go would be if you're chambering new; and if it closed on a no-go then maybe you carefully size your brass to not over size it to Saami min.

Trouble is: without the field before firing you don't know if it has changed after firing. Gunsmith can tell you. Best idea and thanks for the response. Pleas elect us know what is found.

-Mac

 

[Clint08]

Maximum velocities for the 6.5X55 are in the 2700 fps range for 140 grain bullets. You are lucky you didn't get a face full of gas! I don't know the loading specs for the powder you mention, but I HIGHLY doubt they recommend loading to 2900 feet per second. I suggest you get a good loading data book and stick to the maximum loads shown therein.

I would agree and the Hornady book velocity was 2650 for a stouter load. The powder manufacturer’s load was 2 grains hotter, also using the 52,000PSI standard. Had no intentions of reaching 2900fps and when I decided on 48grs I reviewed Lee data, Hornady data, the powder manufacturer VIHT, and loaddata.com. The charge was above starting loads but these are all 52,000PSI max loads being published and in no way close to enough pressure for a blown primer.

 

[358WCF]

Unsure if you're a new loader, a new member, or both. The simple things catch us all sometimes, but not usually to the extent of locking the bolt & wondering why. The seemingly normal 1st shot, then a 200+fps increase with the same powder charge is a little perplexing. A new to you rifle? Wondering if you cleaned any grease or cosmoline out of the bore & chamber before firing? Wondering what device was used to measure powder charges?

1-Starting loads are called that for a reason.
2-All brass is not the same internally.
3- Not saying that you did, but don't confuse the crusty old 6.5x55 with 6.5x55 SE or SKAN. Same case, different animal.
4-Back in the day most all 140gr 6.5 cup & core bullets could use similar powder charges. It just isn't necessarily so any longer.

Nosler lists no data for the 140 Accubond with N165 that i could find.

The loads in Hornady #11 use Hornady/Frontier brass. How does the Norma brass compare in internal capacity? Their start load is 43.1 gr. or approx. 10% less than max... good idea with an unknown rifle & new to you mismatched components. Do you know the difference in bearing length between the Nosler & the Hornady bullets? With a known to be less than "modern" rifle, why start with a max or near max load in different brass with a different bullet even if the bullet weight is the same?

Per the VV 2019 reloading guide they used Lapua brass. Again, what is the internal capacity difference between Lapua & Norma? VV also has no data for the Nosler bullet. All bullets listed from 139 to 140 gr. the start load is between 39.4 gr & 46.3 gr. The max loads are between 46.3 gr & 50 gr. with quite a few less than 48 gr. With a known to be less than "modern" rifle, why start with a max, near max, or maybe over max load in different brass with a different bullet even if the bullet weight is the same?

 

[KMart]

From VV load data
6.5SE/Skan 139 Scenar
Max

N165

Start

44.1

2536

Max

50.2

2831

6.5 Swede 140 Sierra

N165

Start

46.3

2513

Max

50.0

2735

 

[DGP4]

What is most perplexing is the fact that the third shot was over 200 fps faster than the first! The only thing that can cause that is the powder charge. Are you sure that you didn't overload the third cartridge? I can't think of anything beyond the powder that would cause such a spike in velocity! BTW, be aware that many loads listed in reloading manuals are for a modern firearm and not for an old military action. I shoot a lot of C&R rifles as a collector, and I always start probably 2 grains BELOW the minimum load for just that reason.

 

[Clint08]

Where did you find load and why did you start with such a stout load for fireforming brass?Always start with a moderate load for fireform then you can start your load work. Most new brass will have several thousands of excess headspace so it will fit in most rifles. Starting off with a heavy load while moving brass to fit your chamber size is not a good idea. You should be around 2700 fps with that bullet weight. That first load may have been in a cold chamber and once it gets hot things change quickly. Go back and start over with a fireform load. Maybe 44 grains but consult your loading manual.

I’m going to do just that and actually the gun smith I spoke with today mentioned inconsistencies with N-165. The load data was from VIHT and Hornady but I was using a Nosler Accubond 140gr. The Hornady and VIHT data was for lead jacketed bullets. I bought 2lbs of N-165 for this rifle but have a lb of 4831 and 4350 I’m thinking of trying out. The load data I used should all be capped at 52,000PSI for maximum loads, which I should’ve been under but actually wasn’t close to being under. Lesson learned for sure about starting loads and never had an issue like this in 20 years of reloading.

 

[SBS]

To underscore what others have been saying, max. loads in a manual are only for their exact components (including exact lot numbers) in their exact rifles (not yours). Which is why they spend a large number of pages in a manual explaining all this before you get to the reloading tables. Recently a new reloader complained to me about the results of loading a published max. load in his rifle. Not bothering to read all the info. before the tables, he thought it was all right to pick a minimum or a maximum load or anything in between -- his choice. Remember that while Swedes are the best pre-98 Mausers, they are not as strong as 98's or not near as strong as modern actions. So be cautious with these older actions and also be aware that some powders when they go over the top on pressure sometimes go to extremes quickly. Value your eyesight and fingers and start well off maximum.

 

[Homerange]

Remember that while Swedes are the best pre-98 Mausers, they are not as strong as 98's or not near as strong as modern actions. So be cautious with these older actions and also be aware that some powders when they go over the top on pressure sometimes go to extremes quickly. Value your eyesight and fingers and start well off maximum.

This. ^
Whereas in a modern rifle they are a completely different beast if pushed hard.
There is good reason why 6.5x55 factory loads are somewhat pathetic so to protect these old rifles from catastrophic failure and their owners that aren't aware their actions are weaker.
Reload for these old Swedes with extreme care.

 

[hoz53]

I’m going to do just that and actually the gun smith I spoke with today mentioned inconsistencies with N-165. The load data was from VIHT and Hornady but I was using a Nosler Accubond 140gr. The Hornady and VIHT data was for lead jacketed bullets. I bought 2lbs of N-165 for this rifle but have a lb of 4831 and 4350 I’m thinking of trying out. The load data I used should all be capped at 52,000PSI for maximum loads, which I should’ve been under but actually wasn’t close to being under. Lesson learned for sure about starting loads and never had an issue like this in 20 years of reloading.

Ive got a Swede Mauser in 6.5x55. I would never run 52,000 loads in it. Max loads for it are the minimum loads in the books. No reason to push these old guns. I dont wanna eat the bolt some day.

 

[joshb]

Ditto. Mild loads only in mine.
“The maximum charge from Hornady is 48.6grs”
I would never start at 48 grains.

 

[Old Navy]

Glad you did not get hurt. Even when that gun was new it was not meant for the modern day pressures.

 

[dellet]

I shoot old rifles, so I keep old manuals. Most old manuals, 50-60’s list max pressure for the cartridge in the mid 40,000 range.

Later manuals warn against attempting max loads in the Mauser and Krag actions. Then there is the not so old manuals like the Hornady 9th.



Sorry for the glare, max load is 45 grains.

This is where Quickload pays for itself for every shot. More and more manuals do not list pressures, just min/max. That’s often a dangerous place to be with a pre SAAMI cartridge.

 

[dellet]

Joined the group so I could see if anyone has any ideas on this or possible causes. Bought a Mauser 96 a few weeks back at a gun show and still waiting for a field gauge to arrive so head space hasn’t been verified. Below is the relevant information.

Mauser 96 6.5x55 with original barrel
140gr Accubond
1st Shot: 2708fps (No overpressure observed)
2nd Shot: 2855fps (Possibly slight flattening of the primer)
3rd Shot: 2929fps (Took extensive pressure to open the bolt, blown primer, and headstamp imprinted on the bolt)

Third fired case measured .010 over the unfired case when measured at the head. Shoulder had also moved forward .010. I loaded a total of 5 rounds for velocity testing and every charge was weighed.

This is very troubling and a huge warning if I read it correctly.

Did the case head actually expand .010” in diameter?

If that is the case check round #1 & #2 carefully. If they show a repeated increase in diameter, what you were doing is slowly expanding the chamber with every shot. Basically you were one or two shots from catastrophe.

It might be worth checking bore diameter and the transition from throat to rifling. I have seen enough old rifles with basically no throat, only a step for lack of better words. You shave off a certain amount of bullet with every shot and leave a ring that increases in size, decreasing your chamber or jump length significantly with every shot. That might explain the velocity increase.