K31 Reloading help again! Bullets are too big?
Alright, so according to a couple manuals and of course the recommendations here I used the .308" bullet for my k31 reloading. I'm using 150gr. winchester boat tails.
Today I went to the range to try a few out and upon loading the cartridge noticed that the bolt would not lock, this is normal for some hand loads, even if they are full length sized as these were. So I pushed harder and could not get the round chambered. I pulled the bolt back and the round came apart on me with the bullet stuck in the chamber. So I used a cleaning rod and pounded it out. I noticed that the bullet had scratched on it from trying to be forced in. So I tried another hand load and it also did not work. I then grabbed my friends k31 and it also had the same issue. I went home and slugged the bores of the rifles and they are .305".
I'm not sure what to do here. The other dimensions of the cartridge were all within spec. Measuring PP and GP11 the bullet sizes were .306" and .300" respectively. Any recommendations?:surrender:
It's all been said before - in detail
Quote:
Originally Posted by
Patrick Chadwick
"If you have not already done so, you now need to acquire a length of 1/4"x24tpi (or 6mm x 1) threaded rod with 2 nuts that is long enough to reach from the muzzle right down to the block face when the action is closed, and still leave a bit sticking out of the muzzle for the two nuts. This is going to be used as a simple, but very effective "depth gauge" for checking head clearance (NOT headspace!) and establishing the seating depth and appropriate load for your cartridges. "
So let's find out how to use this home-made depth gauge! To make it a bit easier, I have gone through some of the steps with one of my own rifles. It is the Boer Mauser, which I selected because a new member on the Mauser forum has a problem that can be narrowed down by using this measurement technique, and I am using a bit of creative laziness and writing all this just once. Place the rifle on its side on a table. Cock the action (i.e. do not fire it - we do not want the firing pin to protrude) Insert the threaded rod until it touches the bolt face (block face for the RB) Run down the first nut until it just touches the muzzle, while keeping the rod in firm contact with the bolt/block face. Use one hand to hold the rod in contact, and run down the nut with the other.
Now, without disturbing the first nut, run down the second nut until it just touches the first. Make a mark with a felt-tipped pen on both nuts. You have now "zeroed" the depth gauge. I know this is a bit of a 3-hand operation, and I had to use one to take the pics. But with some practice you can develop a feel that lets you measure accurately enough for the present purpose. Now open the action (remove the bolt) and insert a bullet into the chamber. Use a rod, pencil or whatever to push the bullet into the chamber until it is touching the transition cone - the throat. This will push the threaded rod back so that the two nuts are now some way from the muzzle.
Now, without disturbing the second nut (further from the muzzle) run up the first nut until it just touches the muzzle again. This requires some practice, as you need to sense when the rod just starts to lift off the tip of the bullet in the throat. The distance that the nut has moved is the overall cartridge length (OAL) that would be required to have a bullet that just touches the lands before being fired. Now withdraw the rod some way, so that you can use calipers to measure the distance between the nuts. Clamp the caliper jaws and use the calipers as a gauge to see how your chosen bullet and cartridge case would match up. The results can be very illuminating!
Firstly, with the Sierra 168 gn boat-tail bullet As you can see, the base of the boat tail will lose contact before the tip of the bullet engages the lands. That means gas blow-by (leading to throat erosion) and the bullet tipping in the free-flight phase, being rammed into the throat and engraved on the skew, with the result that, even if you have a perfect bore and muzzle, it will go way off course and possibly keyhole.on the target.
Secondly, with the Sierra 140 gn flat-base "spitzer" type bullet. In this case, although the bullet is considerably lighter and shorter than the HBPT of the same weight, the fuller nose means that it touches the lands while about 1mm is still in the case neck. It will perform better than the boat-tail (which is why I purchased these bullets) but is still barely adequate (which is why I am going to try some that are even longer). The Norma 170 gn Vulkan, Hornady 154 gn or 175 gn Interlock, or Speer 160/175 gn Spitzers or magTips would be possible choices.
For nitro-powders you can back off this theoretical OAL by about 10 thou, and take that as a first-approximation ideal length. (Do NOT try for a much smaller value, or even zero, as bullet and seating tolerances will lead to a maybe/maybe not contact between bullet and throat, leading to unpredictable pressure variations etc). Of course, in this case it is impossible to get anywhere near the ideal length, as there must be sufficient bullet in the neck of the loaded cartridge (about 1 caliber length) to ensure reliable and consistent seating. For black-powder cartridges, the short, sharp transition cone usually makes it possible to use the ideal length, but you need to back off about 1 mm / 40 thou. This is necessary because fouling is always worst in the throat. If you seat the bullet too close to the lands, then the first shot will be OK, the second will require a good shove to get it to chamber, and the third will need a hammer.
Rolling Blocks are touchy in this respect, as there is no bolt camming action to help you. So give it some space, unless you want to give the bore a complete clean after every shot. The measured values for the Argentine chamber and the picture of the throat lead me to expect that the bullet will need to be seated with a good portion within the case neck. I would like to see the results of this measurement before proceeding to the actual loading of the cartridge. That's all for tonight folks! Patrick
To which I would like to add three comments:
1) Go to the thread on restoring the Argentine Rolling Block, and you can get this with the photos. This method really, really works, and will save you a small fortune in headspace gauges etc.
2) Latigo, you were being a wee bit unfair to Gunner, even if jokingly. I think that the back-off need to be more like 10 thou than 2 thou from the contact position. I have measured 30-06 rounds prepared with Lapua Scenar bullets in an RCBS competition die, and the spread was more like 4 thou. 2 thou off the lands will mean that, in practice, some bullets will touch the lands, maybe causing flyers because of the pressure rise. I think it is better to be sure that none are touching.
The 30-06 rounds used for the competition target I have posted on the M1917 and Range Reports forums were prepared according to the above method - with 10 thou back-off. The consistency of the results is proven.
3) can someone please tell me how I can make a link to an existing post, to save all this copying!
Patrick
:wave:
Well, this is how I do it...
Quote:
Originally Posted by
Latigo
The cartridge OAL means nothing to me at all.
Well it will if you can't get the cartridge into the magazine :lol:
Seriously, neither Uncle Ray's Q&D method not my SbP method will give the answer to the last thou, and I have seen myself how meplats vary. I already pointed out that even with the excellent Lapua Scenars the OAL varies with a spread of about 4 thou - for that very reason - the RCBS competition seater is indeed indexing on the ogive, as do most (I'm not going to bet on all ) top punches (odd name, one doesn't punch with it). However, we all refer to OAL, and you are right to point out that that is not what we really mean (or ought to mean?).
But these methods put you quite close for a good first approximation. When I have made such a measurement, I seat the very same bullet in an empty case with the top punch screwed right out, and then by trial and error screw down the top punch and re-seat it until the OAL is about 20 thou longer than the SbP measurement. I then "paint" a black ring around the bullet with a felt marker pen, let it dry, and then reload the case in the rifle. When the cartridge is removed, the forcing cone, lead, transition, throat or whatever you like to call it will have made tiny marks at the contact points. Again, reseat a couple of thou deeper, paint and repeat, until no marks are produced. At this point the seating of THAT bullet is such that it is just off the lands.
As already remarked, since every mechanical item has tolerances, I like to take that setting and back off 8-10 thou (.2 - .25mm) for the final setting. For BPCRs I make that 20 thou, because of the fouling that builds up in a competition where you cannot thoroughly clean the rifle between shots.
If you like, you can go for 5 thou or even less. It depends how much confidence you have in your equipment. But on simple mechanical considerations, a seating clearance that varies from say 8 to 12 thou is going to cause less shot-to-shot pressure variation than one that varies from +2 (i.e. just free) to -2 (i.e. cammed into the lands).
Patrick
:wave:
