k31 and 284 brass question

[30hrrtt]

My son has a k31 and is keeping it at my place as he is back in school. It hasn't been shot in a few years. I was going to check fit with a couple cast boolits. I went through about 50 fired cases and the cast wouldn't come close to going in at .309.

I then tried with a couple varieties of jacketed .308 and could just get them in. Some took a little preassure. Some went in easily but NOT loose.

It indicates to me that even with the jacketed bullets he was shooting, there is not room in the neck chamber for expansion. There should be a least a couple thousandths.

For anybody using 284 brass with either bullets or boolits, do you neck turn your 284 brass?

[Bob S]

For anybody using 284 brass with either bullets or boolits, do you neck turn your 284 brass?

I have been using 284 brass exclusively for a small collection of K31's and 1911-types for 11 years now. I have not found it necessary to neck-turn cases. The most likely cause of resistance to chambering is that the bullets are not seated deep enough for the "throat" of the K31; and/or the shoulder of the case was not pushed back far enough during the reforming to 7.5x55 or subsequent resizing.

Resp'y,
Bob S.

[swheeler]

No nk turning needed, I have shot .309" and .310" cast in 284 WW super brass.

[30hrrtt]

was not talking about chambering

i was going to put a cast in long and then chamber
then with a measuring rod, measure the longest col with boolits touching rifling

the boolits were snug in the fired cartridge case
boolits are usually a little loose in a fired case and I slightly deform the case to hold them

thanks

[mike in co]

k31's are not 308's
k31's have no throat( a slight bevel..40/50 thou long)
284 brass necked up to 30 works fine

k31 are closer to 306x 296 than 308 by 300

the no throat design is based on thier dual dia bullets( one dia in the case and smaller forward of the case) which is why thier ammo chambers and most 308 ammo must have 95& of the 308 dia of the bullet back in the case.


most llikely your rounds will not chamber because of above, not case neck dia/clearance

mike in co

[Bob S]

the boolits were snug in the fired cartridge case

thanks

What loads were fired in the cases? Full power jacketed loads, or light cast loads? How many times have the cases been fired since they were formed to 7.5x55? Have the case necks ever been annealed? What is the OD of the neck of your cases that have been fired with service-equivalent loads?

You could have a tighter neck than usual. I have not seen this with any Swiss and it would be highly unlikely especially in a K31, but it's possible if the chambering reamer was close to the end of it's useful service life (worn). A chamber cast should be done and the neck area should be carefully measured. It would also be useful to measure the neck thicknesses of your particular 284 cases with a tubing micrometer.

Are you located anywhere near Quantico? (Edit: I guess Milwaukee isn't anywhere near Quantico.)

Resp'y,
Bob S.

[chuebner]

Both of my K31's slug at .297 X .307 and I normally load .309 cast. I use the Lee collet neck sizer and Lee universal expander dies in the reloading process. The fired cases are flared just enough to clear the gascheck. Obviously these are not a slip fit and require a slight amount of pressure to seat. Yesterday I made it out to the range for awhile and using the modified RCBS K31 sil. boolit from the group buy here, I was able to keep them in less than 2" at 100yd. using 9gr. Unique. I'm pleased since I may have found my best load for the upcoming CBA Military Rifle Postal Matches.

charlie

[jh45gun]

I size my cast bullets for my K31 at .309 and they work fine and I also use 284 brass and I do not neck turn either. You just have to make sure your bullets are seated deep enough to chamber.

[jonk]

I have 4 7.5 Swiss rifles and none have this problem.

Personally I would size and flare and load. If they chamber, I wouldn't worry about it. Obviously if he has shot it there is enough neck room or he would have noticed pressure problems.

[Multigunner]

Could be a build up of hard fouling in the chamber neck.
My No.4 showed pressure signs and a swollen primer pocket on one occasion till I throughly cleaned the neck with a scrapper I made from brass tubing.

I cut angled slots down each side and filed teeth in the circumference of the end.
When turning it into the hardened fouling black stuff started peeling away in thin strips. The stuff was about the consistency of an old phonograph record, and from what I understand of the products of combustion of various smokeless powders and additives the materials may be similar in make up.
Old Milsurp powders salvaged from condemned lots of ammo were once recycled to make various types of glues and varnishes. When baked onto steel the surface is usually slick and even to the eye, and is not that easy to spot by casual inspection. Chamberbrushes can hold down this build up but only if rifles are throughly cleaned soon after firing, something seldom possible in wartime.

Graphite, Calcium , and numerous other moderators anf flash suppressants greatly increase hard fouling deposits left by Milsurp ammo compared to sporting ammo.

Once a thin skin of fouling forms pressure on firing pushes more fouling down around the neck driving the earlier deposits ahead of the fresh deposits. The more that builds up the faster it will continue to build up.
Laquer sealants around the case mouth add to the situation.

A couple of thousandths difference in bullet diameter mean less in bullet to bore fit than the effect on outside neck diameter of the loaded cartridge.

Bullets begin to bump up while still in the neck, if there is not sufficient clearance pressures can skyrocket before the bullet clears the case neck.

Old cupro-nickel build up in the throat and leade can also cause problems.

[jack19512]

For anybody using 284 brass with either bullets or boolits, do you neck turn your 284 brass?








No, never have.

[mike in co]

For anybody using 284 brass with either bullets or boolits, do you neck turn your 284 brass?

to repeat...no

expand to 30 . load and shoot....done

mike in co

[runfiverun]

maybe there's a reason they call them 7.5's and not 7.62's
i think the swiss can measure.

[NickSS]

I also use 284 Win Brass in my K31 and I do not neck turn nor ever felt the need to. The biggest problem with loading for the K31 is its short neck. The Swiss use a long 173gr VLD type spitzer boat tailed bullet. I have found no generally available bullets that are like it. As a result all my loads require seating the bullets deeper than I normally do in other 30 cal rifles. For cast bullets I generally use the Lee 160 gr AK bullet sized to .308" it works very well with my rifle.

[jonk]

maybe there's a reason they call them 7.5's and not 7.62's
i think the swiss can measure.Yes they can... as can the french. But whatever standard they are using, maybe measuring across the bore and not the grooves, it still slugs to .308" nominally.

[mike in co]

Yes they can... as can the french. But whatever standard they are using, maybe measuring across the bore and not the grooves, it still slugs to .308" nominally.

i will not say you are wrong, it could be out of spec, or worn, but the spec is .296 x 306 if i recall correctly. 308 bullets/loolits will shoot but must be stuffed deep in the case as the chamber has no real throat.( if you truly have a 308 you should be able seat conventional 308 bullets with .300 lenght of body out of the case...try it)
as i said before regular bullets do not "seat" at "normal" lengths....cause everything 308 in dia must be in the case minus about 50 thou.


nickss..,,"The biggest problem with loading for the K31 is its short neck. " not short NECKS..short THROATS...

mik ein co

[45 2.1]

I've shot 284 brass since the 70's in all the older Swiss rifles. You have to work the action firmly in some of the K-31s. You'll find the K-31 has a different arrangement than the earlier Swiss rifles in that the chambers neck length is a lot longer, and the throat is quite abrupt, than the cases neck is. Try the RCBS 308-165-Sil boolit sized 0.309" seated to the base of the neck and tapered crimped lightly in front of your load of choice (11.0 to 11.3 gr. of Unique works well). That should work well for you.

[30hrrtt]

Thanks for the replies. I do understand the throat issues of the K31 and I loaded the ammo for my son a few years ago. They were full power loads.

My FIRED case necks are measuring .340 outside diameter.
My 284 brass thickness is measuring .016.
Times it by two and I have a .308 neck opening on the FIRED case.

I am hoping to slug the bore and do a chamber cast this weekend.

What are some of the measurements you guys are getting on your fired case necks, outside diameter?

[mike in co]

thanks for the replies. I do understand the throat issues of the k31 and i loaded the ammo for my son a few years ago. They were full power loads.

My fired case necks are measuring .340 outside diameter.
My 284 brass thickness is measuring .016.
Times it by two and i have a .308 neck opening on the fired case.

I am hoping to slug the bore and do a chamber cast this weekend.

What are some of the measurements you guys are getting on your fired case necks, outside diameter?

remeasure the brass neck thickness.....mine is 11/12 thou.....

[Bob S]

but the spec is .296 x 306 if i recall correctly.

The European method for specifying internal dimensions is to specify a bore diameter and a groove depth. The tolerance on new 1911 barrels was 7.54-7.60mm, grooves 0.13mm deep. New K31 barrels were 7.50-7.57mm with grooves 0.15mm deep. This means groove diameters within tolerance will range from .307" to almost .310" and acceptable new bore diameters run from .295" to .299".

Resp'y,
Bob S.

[30hrrtt]

Mike in CO

I think I have found answer to my concern and it might be my brass. I did remeasure and they are in deed 16 thousands. This is after approx. 2 firings.

I opened a new pack of Winchester 284, purchased 5 - 6 years ago. They are between 17 and 18 thousandths.

What are others getting for the neck thickness of Winchester brand 284 brass?

[mike in co]

The European method for specifying internal dimensions is to specify a bore diameter and a groove depth. The tolerance on new 1911 barrels was 7.54-7.60mm, grooves 0.13mm deep. New K31 barrels were 7.50-7.57mm with grooves 0.15mm deep. This means groove diameters within tolerance will range from .307" to almost .310" and acceptable new bore diameters run from .295" to .299".

Resp'y,
Bob S.

my calculator says 295-298....
then there is slugging them and see what you get.....
and then there is the whole no throat issue, just an entry radius.
( no throat because they use a dual dai bullet)

[Bob S]

FWIW, I have Swiss with groove diameters from .3064" ( a 96/11) up to .3092" (a K31 rebarreled in 1955).

Resp'y,
Bob S.

[mike in co]

FWIW, I have Swiss with groove diameters from .3064" ( a 96/11) up to .3092" (a K31 rebarreled in 1955).

Resp'y,
Bob S.

bob,
can you seat 308 bullets in this gun ?( that is putting 308 dia forward of the neck ?)
all of mine are small( closer to min spec........

mike in co

[Bob S]

Let's see if I remember to push the "POST" button this time. :confused:

Mike,

Yes. The .306+ rifle is a 96/11, with a throat. If it was a K31 with a non-throat, all bets might be off. But with that 96/11, no problem with .308 jacketed or .309 cast.

I found a box of my "universal" jacketed load, so called because it will chamber easily in every 7.5 x 55 that I currently own. (I have another one coming, but it's not a K31 or a Schmidt-Rubin ;-))

http://img.photobucket.com/albums/v76/BobS1/Swiss/7pt5universal.jpg

The bullet is a pulled Sierra 180 grain Match King "Hague Convention" bullet. It came from Navy A-190 ammunition (.300 Win Mag). I have a couple of buckets of them from both the A-190 and some 7.62 that Alliant put together for us, but was never assigned a NALC. The reason they got pulled was that they started to yaw badly after about 800 yards. They are perfectly fine for short range shooting ... 200 and 300 yards. Beer cans are not the only things we recycle around here. :mrgreen:

The parallel midbody that protrudes from the case is .3082", and extends about .055" forward of the case mouth. If you look carefully by the red arrow, you can see the marks from the bullet puller. That gives a visual indication of the length of parallel midbody.

For those asking about using .284 cases, the case of the cartridge pictured is a .284 freshly expanded and resized in my pre-historic CH FL sizer. The mark that you see on the neck at the green arrow shows where the .284 shoulder was, and gives a visual indication how much the shoulder has to be set back for 7.5x55.

Resp'y,
Bob S.