Checked chamber lengh for my 1893 Spanish Mauser and got 3.165" to the lands...

Hey guys,
I'm taking this ole girl to the range and getting massive groups like10" at 50 yards. I got a case and cut 2 slits and dropped a bullet on top then chambered to see where the lands pushed it back to and got 3.165". Should I be loading at 3.13" vs 3.00"? Could this be the source of my inaccuracies? I've only shot it 3 times. Once with the rear iron sight and got maybe the same or maybe 8" spread I forget. Then put on the rear sight rail which I hear isn't that great but I checked it after shooting and it's on there solid. I slugged the bore and got .276 and .275" should be the factory bore so pretty close still. I see visible crisp rifling. Has anyone noticed their old Mauser to have a "deep throat"? Did you also need to load a lot longer?

If the case length will permit it, then seating the bullet to be about 0.010“ off the lands would be a good start. However, if the rifle has a deep throat this may not be possible, as there should be at least 1 caliber of bullet length in the case neck to hold it reliably and consistently. A very good reason to use Spitzer or round-nose bullets. In my experience boat-tails are useless in Mausers of this vintage, as you just cannot seat them properly without being way off the lands. These old Mausers were designed for bullets with a good cylindrical back end, not boat tails.

That's a good point. I should have got the flat bottom bullets. I have a few that someone else sold me but I'll probably need to use up what I have or try to trade. When I shoot 123g .310 bullets with Enfield they shoot fine so as long as I get get a snug fit I should get better groups. I'll report back with the results. Thanks Patrick.
Jeff

You need to get the groove measurement , that is most likely your problem . What bullets are you using ? The groove will matter much more than the throat .

Thanks Bob. The spec for the barrel is .275" for a 7mm Mauser and it slugged at .276" at the lands which I'm told is fine. The bullets I'm using are .284" but are 139g boat tail bullets which seem to be too short for loading long just off the lands but they seem to barely work. I loaded some at 3.135" COL but I want to get the 173g flat back that should easily load longer to maybe 3.15". The grooves are supposed to be .285" but not sure what mine are. The rifling looks good visually. I'll shoot them long and report back what the results were.

You need to know the groove size . If you have a .288 + groove your short boat tails will not ride the rifling straight and you will have poor accuracy . I have seen that a lot on 7mm military rifles . I once bought a M-95 from a guy who was shooting Rem 139 BT's with the same result as you , he sold it cheap since it would not shoot . With the right bullet in handloads it shot 2 inch groups at 100 for me . What something is supposed to be and what they really are can be two different things .

Thanks Bob, I'm hoping that's the case. I don't plan on selling it and I have some flat base bullets to try. I got a care package from a felling 7x57 guy <3 hehe. 139g spire point flat base, 120g spire HP flat base, 140g spt X flat base, 150g spcl flat base. I'm going to order some 173g and hoping they are flat base so waiting to hear back from the shop. I was thinking seating out would help and didn't realize bullet obturation would help also. If I load close to the lands with flat base bullets crossing toes that does the trick. Thank you

Something else that will help with the fb light bullets is a light load with a fast burning powder . That will give them a " kick in the pants ' to help with obturation , the light bullets are usually varmint types with thin jackets and soft cores .

I'll use the WC747 I have. It's a little faster than W748. It's made in the same factory. I already tested it for safety with the other 139g bt bullets so it's good to go. Thank you Bob

I used my homemade took which is a case with 2 slits so I can pop a bullet on and test to see how long before it hits the lands. I must have had some crust or something before or just didn't notice. I put a 140g flat base spire bullet and it measured 3.26". After chambering it still measured 3.26". I then got a 150g hp fb bullet and it measured 3.33". After chambering it still measured 3.33". Do these throats open wide then tapper down or mine is just so worn I just need to load as long as possible before the bullet falls off? When I used my bore scope things looked to be in the right place. I could see the shoulder and neck in the chamber and where the neck ends. Things probably weren't precise in 1893-98?

To put it quite bluntly (without intending to be rude!) - Stop messing around with plinker bullets!

I copied this from a previous thread on the same problem (in a Mosin-Nagant 91/30 sniper):

".. A possible problem is that the throat of the rifle is deep enough that the boat tail is coming free of the cartridge neck before the bullet is engaging the lands. This can actually lead to a worse internal ballistic performance and group size than with flat-base projectiles, as the gas blow-by on the bullet can cause it to be engraved with a slight skew**. Check the absolute maximum OAL you can use (with the bullet touching the lands) and if, in this position, the start of the boat tail is out of the case, stick to flat-base. That is precisely the situation with my 91/30. So the direct answer to your question is: yes I have tried HPBT, but the flat-base round-nose or spitzer types fly better in my rifle!

*Get the Sierra book for detailed trajectory values.

**I suggest that you get out your pocket calculator and work out how much skew over the length of the parallel section of an HPBT corresponds to 1 MOA. It is very, very, small."

and next day:

"Ah well, since no-one else worked it out yet...
Using the old rule of thumb:

1 MOA corresponds to 1" at 100 yds.
so
1 MOA is 1/1000" at 1/10 yd or 3.6"
and over half an inch (the approx. length of the parallel section on an HPBT)
1MOA is 1/1000" divided by 3.6 x2 or 7.2

About 1.4 tenths of a thousandth of an inch. Small enough for you?

So now it is clear why the bench-rest boys measure things like bullet run-out in the case.
And why they try to get the "slop" of the neck in the chamber down to well-nigh zero.
And why neck sizing your fired case, leaving an ever-so-tiny unsized ring at the bottom of the neck that provides automatic centering of the neck in the chamber improves accuracy.

It's not just nit-picky fiddling around - it really can make a difference - if you and your rifle are good enough."

Use the longest bullets you can find for the 7x57. Flat base bullets. Something in the 160-180 grain range. For instance, the S&B "SPCE" bullets produce excellent results, as they have a long cylindrical section up to the step. They also cut very clean holes!

Bob has mentioned using flat base bullets which I will use. It's the obturation he was saying I need to make sure happens so the bullet actually goes into the grooves. Loading much longer and using the heavier bullets the rifle was designed for will probably help also. I bet I get at least fist sized groups next weekend. I'll report back after. I consider plinker bullets anythijng not expensive so I think flat base bullets don't have to be 50 cents each right? The plinkers I plan on getting next are 173g flat base bullets that one store said they should have in stock this week. I'll just be plinking out to 50-100 yards so not long range. I'm silly so I googled plinking and it actually has a Wiki page hehe geez.
"Plinking refers to informal target shooting done for pleasure, typically at non-standard targets such as road signs, tin cans, logs, bottles, or any other homemade or naturally occurring target"
Thanks Patrick, at least I know it's probably not a broken rifle.

"173g flat base bullets " - that's not plinkers, that's serious bullets. By plinkers I meant those lightweight things.

BTW, I have seen a diagram of what happens when a bullet is engraved with a skew. The trajectory becomes a spiraling spiral (or coiled coil) pattern, and it is absolutely impossible to predict where the point of impact will be in the spiral motion. So grouping is very, very bad and cannot be improved by fiddling with the load etc.

An unevenly worn muzzle or damaged bullet base has the same effect. In this case, the skew arises when the bullet receives an asymmetrical impetus on leaving the muzzle.

Yeah I call cheap bullets plinkers regardless of weight since plinker just means not serious target shooting vs match grade. All bullets are serious but match grade would be non plinking. I have some expensive 125g flat base match bullets for my 308 that are much much more serious than my and cheap 150 and 168 grain bulllets but sounds like you use weight to define plinking vs serious match stuff it's all good. I can't wait to shoot next week and especially if I get the 173g bullets. Thanks again Patrick

Some of my very best target load for 7x57mm military rifles were light loads with the very light bullets of 100 to 115 grains . PERIOD . I am talking about 1 to 1.5 inch 5-shot groups at 100 yards shot on demand during rifle matches . So do not tell me it does not work . I am talking about 1000's of test rounds through over 50 different 7mm rifles .

Thanks Bob. I'm sure the flat base and loading a little farther out will help. It's like you said I need to make sure the bullets obturate into the groves. I took a couple pics of the muzzle and the rifling looks fine so I'll try to post here. I was wondering if you would notice the previous posts with someone thinking things lighter than 173g is just a plinker regardless of quality, match grade, price, etc.. He probably just meant to say heavy which in my case doesn't matter as much as the flat base should help but the longer length I'm sure will help also in my rifle. I dropped a bullet into the chamber with the rifle pointing down and the bullet drops past where the neck ends. In your experience have your other rifles done that and still shot fine?
Someone on another forum told me about counter boring. I'll post the second picture also. One of the grooves seems to fade out which is probably causing some issues also. I'm asking my local gunsmith if he counterbores and how much. Video below does a good job explaining to me in case anyone else searches and finds this thread it could help them.
Military Surplus Firearm Collecting - Episode 1: Counterboring. What is it, why, and is it bad? - YouTube

Took better pics of the rifling at the end. Maybe they fade in the last couple millimeters so maybe not too bad to need counter boring?

All chambers have a throat so the bullet has some jump otherwise to engage the rifling I.E cammed into it by the bolt would cause a very dangerous pressure level. I would also check the crown of the barrel to ensure no damage has occurred bit hard to tell as your pics are pretty fuzzy.
If one land does end before the others then the bypass of gasses may cause a skew and upset the bullets flight, I gather the bedding is good and the H/S in spec sometimes it can be a very simple thing causing a group dispersion.

When you do get it sorted I found a ladder test is the quickest way to find a load that groups you can then work on getting it even tighter with development, hope you get it sorted I know what its like to own a shotgunning milsurp my sniper T was one such animal.

Thanks Cinders. I'll load up some 175g flat base tomorrow when they arrive in the mail. Between longer bullet, flat base, loading longer COL that will probably help. I might try the brass round headed bolt and lapping compound to clean up the end of the muzzle if there is any small burs I can't see. I bet the groups tighten up. I'll post pics

"but sounds like you use weight to define plinking vs serious match stuff it's all good."

Apologies to all if I caused irritation. I shall try to avoid the word "plinker" in future!

Ladder test?

You start at say min X grains then go up in .5 grain increments to the max at some point the 3 shot group will tighten up then open out again.
You can also use other data from others so if the published load is X then you have 2 grains either side of that E.G say the sweet spot published reload was 40gns then you'd load 3 rounds at 38 - 38.5 - 39 - 39.5 - 40 - 40.5 - 41 - 41.5 - 42 * provided the upper loads do not produce excessive pressures or exceed maximums.

I used it on my 6.5 x 284 & 22/250

Thanks. I thought so but your explanation makes it very clear.