.310 Cadet accuracy

  • 967 Views
  • Last Post 18 July 2019
JeffinNZ posted this 12 June 2019

Well, I'm back to square one.

I spent a long time trying to get my .310 Cadet to shoot with smokeless powder and reformed .32-20 brass.  Long story short, the neck thickness was insufficient and on firing the brass expanded and the massive blow by of gas caused leading and NIL accuracy.  Using correct Bertram brass with neck thickness of 11-12 thou solved the issue and fired cases need no sizing as the heel of a CBE bullet is a snug fit for thumb seating.  Instant accuracy.

Of course being an idiot I only bought 20 of those cases and recently picked up another 50 to find the walls are thinner.  ARGH.  9 thou instead of 11-12 thou.  Doesn't sound much but using EXACTLY the same load at 50m the correct dimension old brass shoots 1 inch groups.  The new brass is putting bullets sideways and not on A4 paper! 

The solution will be to hone out the heel of the mould such that it drops bullets that are a snug thumb seating fit in the fired new brass.  The heel will need to be .312 inch.  Ideally I believe Cadet moulds should be hollow base as the original swaged bullet are and likewise .22RF with the hollow allowing the base to slug up to seal the bore quickly.

Cheers from New Zealand

Attached Files

  • Liked by
  • M3 Mitch
Order By: Standard | Newest | Votes
pisco posted this 12 June 2019

hi i run bertram brass and have a cbe mould that throws 319 cast bullets from w/w the heel measures 312 i run 10.5 gr winchester 296 powder it must be the same speed as the original load as the elavation marks are the same i run a pistol primer at 50 y 10 shots measure 30 mm i am experimenting with unquie powder it is grouping about the same

Attached Files

  • Liked by
  • JeffinNZ
JeffinNZ posted this 12 June 2019

PISCO: I am going to have my heel opened out to cast at .312 in 40-1.

Cheers from New Zealand

Attached Files

45 2.1 posted this 12 June 2019

I've used the RCBS bullet and one smooth sided one from a Lee GB. Match your alloy to the pressure level and your shank size won't matter too much. On recovering fired bullets, I found both varieties bumped out to full diameter and shot well (to the sights also) out to 400 yards. Remember, they had the 310 Cadet to train boys in long range shooting.

Attached Files

JeffinNZ posted this 12 June 2019

I've used the RCBS bullet and one smooth sided one from a Lee GB. Match your alloy to the pressure level and your shank size won't matter too much. On recovering fired bullets, I found both varieties bumped out to full diameter and shot well (to the sights also) out to 400 yards. Remember, they had the 310 Cadet to train boys in long range shooting.

In all the original testing with converted .32-20 brass I tried different alloys to no avail. 40-1 shoots superbly with the thicker walled brass so the alloy is not the factor and with the charge of 5gr of Unique pressure will not be particularly high. Thick walled brass = good accuracy, no leading. Thinner wall brass = NIL accuracy and leading. The issue would appear to be the brief instant when the thinner case walls expand to fit the chamber leaving the heel exposed to a blow by of gases much as any under sized cast bullet is. With the thicker walled brass there is no case expansion forcing the gas to stay behind the heel.

Cheers from New Zealand

Attached Files

45 2.1 posted this 12 June 2019

 "With the thicker walled brass there is no case expansion forcing the gas to stay behind the heel."

I've found that to be caused by other reasons, not that though. You really can't have a fixed cartridge and have it keep the powder pressure all behind it, even with absolutely minimum clearance (0.0005" or close to that total clearance). The internet has several videos depicting the gas blow-by leaving the muzzle before a bullet shows up. A breech seated flat base might do that though. It would seem that gas does get by as soon as the neck lets the bullet go before it enters and seals the bore... in whatever order that occurs because it's speculation. If anyone can say what it does with 100% certainty, please do so. You should look pressure curves from the powder you use and pick an alloy that is softer than you think to use for it. The target and bullet you show didn't seal and stay centered... I would say it didn't bump up, which all heeled bullets need to do, not just ride the land tops.

Attached Files

  • Liked by
  • M3 Mitch
JeffinNZ posted this 12 June 2019

That’s not a recovered bullet in the photo. If the alloy is at fault why does the load with thicker walls shoot so well?

Cheers from New Zealand

Attached Files

  • Liked by
  • M3 Mitch
45 2.1 posted this 12 June 2019

That it's not a recovered bullet is obvious... no rifling and it has lube on it. Why does it shoot so well......More guidance for the bullet shank from the case walls. The bullet shank is a little to small or it is too hard to expand to groove size.... that is an observation from what you say and the keyhole on the target. If it could expand properly, it would not keyhole like that. Smaller than optimum bullet shanks tend to do that when they are too hard to bump up..... much like what happens when GC bullets are shot without the GC, but in the Cadets case, it doesn't have enough bearing surface length to help straighten it out.

Attached Files

JeffinNZ posted this 12 June 2019

Exactly the same bullet and alloy with both loads. 40/1 is perfectly soft enough to slug up.

Cheers from New Zealand

Attached Files

45 2.1 posted this 13 June 2019

OK, then answer this question.............Why did you get a keyhole when it is perfectly soft enough to slug up? It seems it didn't with the thinner brass. Recover some fired bullets and see what happened.

Attached Files

Squid Boy posted this 13 June 2019

The only time I have ever seen a keyhole out of my 310 Cadet is when I tried to shoot some undersized bullets meant for a 32-20 in it. I have a CBE mold the drops a 130 grain bullet at .323 diameter with a .310 heel. I use 20-1 alloy and this will put five into a half inch at fifty yards using 4.9 grains of Viht 3N37. It is also very accurate in another Cadet re-chambered to 32-20 but with 5.2 grains of Unique. Seems very strange what you are getting. Squid

Attached Files

Mike H posted this 13 June 2019

This problem of Jeff’s shows how a small change can upset a good performing load,I am confident he will sort it out,though I don’t have a .310 Cadet,I find the discussion interesting.

Attached Files

Squid Boy posted this 13 June 2019

Just for fun I dug out the only original Kynock 310 Cadet cartridge I have in my collection. A hollow point no less. The case measures 1.120" and is .324" diameter measured at the upper end of the neck. The bullet is .318" diameter and the COA is 1.567". It's the only one I have so I won't be dismantling it but I thought this might be interesting. Squid

Attached Files

  • Liked by
  • M3 Mitch
JeffinNZ posted this 13 June 2019

Hollow base bullet?

Cheers from New Zealand

Attached Files

Ken Campbell Iowa posted this 13 June 2019

hey jeff ... numbed minds want to know ::  before you hone out the base on that naughty bullet mold .. how about just drilling out some hollow bases with a drill press ?? ... about 3/16 inch dia., 1/4 inch deep should work.  your drilled holes might not be perfect, but if they improve, it might show the right direction.

to do it right, it would require a dedicated die set with a swaging pin or a drill guide .  easier to hone the mold .

i always wanted to try drilled out hollow bases, but so far have never had the problem you are finding.

**************

also, remember that those glorious 22rf bullets have a very short heel ... yours has a  very long one, almost half the mass is unsupported at ignition/brass expansion.  my benchbuddies assure me that the brass expands before the bullet moves, and just leaves it hanging there in mid-air ...

which might make it interesting for you to breech seat some shots just for fun ... ?? need a push rod in a case for a martini ??

interesting thing you have there .

ken

Attached Files

Squid Boy posted this 14 June 2019

Jeff, no, a hollow point. Sorry if I wasn't clear. I had Accurate make a mold from my design, that is longer weighing 141 grains. I wanted to try having the bullet engage the rifling without breech seating. This one engages by about .010" on my rifle and the breech block finishes the job of loading. It shouldn't be very stable according to Greenhill but the Miller says it's OK and so far they are all point on at 100 with no sign of tipping. I just started testing and it's not quite as accurate as the lighter CBE but I think it may improve. Thanks, Squid

Attached Files

  • Liked by
  • M3 Mitch
tony1960 posted this 15 June 2019

Jeff, I must say that I concur with you. The case wall thickness is critical when dealing with this and other straight walled cases. Now that you have fire formed the new cases have you measured the inside diameter of the cases? Might be of some use to find out if you have to bump up that base, the other alternative I have thought of is to wrap PTFE tape around the heel to make a snug fit in the cases. Or would a cardboard wad under the base help with the leading? it may be just enough to offer some firewall. I will find some time tomorrow to measure my case walls and ID, I have newish Bertrams and have only fired them 3 times.

 

cheers

Attached Files

tony1960 posted this 16 June 2019

Jeff, I managed to measure all of my 310 Bertram brass today, both wall thickness and ID after firing in my chamber.

The wall thickness averaged out at 0.0095 but ran between 0.009 and 0.01 with the majority on the thicker side. I would confidently say they are 0.01. I also measured my fired brass for ID without sizing and they all ran an average of 0.316, my projectiles have a heel of 0.315 - 0.317 so they are a nice fit by hand. When I chamber the case they have a nice feel on closing. I hope this helps mate.

 

Tony

Attached Files

  • Liked by
  • JeffinNZ
barra posted this 24 June 2019

I just made up some rough swagged bullets my using a plugged case to hold the lube bullet.

i have a old chamber cut back to use as a size die when making new brass or sizing fired brass.

by putting it into the sizer and using a rod . I tapped the rod to fill the throat .

the base is also expanded by the case being kept solid by the die wall.

No magical bullet grouping happened but it was not any worse either.

Just putting it out there.

I only get around an 1" at 50 yards which is about as good as I can see to hold anything with a Parkerhale #7 peep.

 

Attached Files

  • Liked by
  • M3 Mitch
longhunter posted this 27 June 2019

Well now that I'm the proud owner of a 310 cadet, I need to learn all about it!

Thanks for writing keep it up.

Jon

 

Jon Welda CW5 USA Ret. 608 797 0056

Attached Files

JeffinNZ posted this 27 June 2019

Making progress.  Heel of the mould opened up and now throwing a heel of .312-.313.  Leading has stopped.  Accuracy still sub par but round holes.  Tried some ACWW today with some success.  More to follow.

Cheers from New Zealand

Attached Files

Show More Posts
Close