.310 Cadet accuracy

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Last Post 05 July 2023

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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

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JeffinNZ posted this 07 July 2019

Frosty morning, Took the Cadet to the range to verify some sight settings. This is 4 shots at 50m with the new, altered bullet/mould and ACWW alloy. Two in the white are the 50y setting, two in the black sights set between 75 and 100y.

Cheers from New Zealand

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barra posted this 01 July 2023

Longer brass may help.

I try for a snug fit.

‘how is the bore condition?

I bored out my base band on the RCBS mold to 0.315" to fit my 32-20 shortened brass.

Shoots well without having to resize or tamper with brass.

I cast on the softer side and use plenty of soft lube.

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linoww posted this 02 July 2023

I just got back shooting 50 rounds and no tippers! it's so frustrating because it's intermittent.

"if it was easy we'd let women do it" don't tell my wife I said that!

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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

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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

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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.

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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

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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

"Squid Pro Quo"

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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

"Squid Pro Quo"

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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

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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.

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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

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pisco posted this 08 July 2019

hi that’s the go jeff you would have to be happy with that i had a cadet years ago before any of these sights and i had no idea what i was doing so i sold it now we talk about things like this to people all over the world and it it is so much easier to get information

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linoww posted this 01 July 2023

bore is as mint as can be.The case length is 1.1" and pretty close but not quite to full length. Bullets are my plainbase 32-40 alloy of 20-1. I thought about heel diameter as well.I may open up the heel thanks!

"if it was easy we'd let women do it" don't tell my wife I said that!

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JeffinNZ posted this 01 July 2023

Longer brass is often the answer.

Brass for the .310 Cadet | Cast Bullet Association | Online Forum | Bullet Casting Forum

Cheers from New Zealand

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linoww posted this 02 July 2023

it's the RCBS 120 cadet bullet,not a 32-40 bullet.

"if it was easy we'd let women do it" don't tell my wife I said that!

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barra posted this 02 July 2023

I would be putting the cleaning rod down the muzzle of the closed action and marking the rod at the muzzle.

‘I would be then seating a cast bullet and measuring the distance the rod goes down between the muzzle and that line.

That should be your overall length of loaded round.

I would personally test with breachseated bullets and a loaded case before I opened the heal of the mould.

the extra length may be a bit narrower.

‘With everyone making and using reamers for fitting the swapped barrels the dimensions can be far from perfect ideal blueprint drawings.

just my 2 cent’s worth.

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JeffinNZ posted this 03 July 2023

Something else to consider is using softer alloy. I cast exclusively in 40/1 for the Cadet. Slugs up great. Approx 7.8 BHN whereas your 20/1 will be nearer 10 BHN.

Cheers from New Zealand

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linoww posted this 03 July 2023

I'll try softer. once I had nearly all bullets tumble. I modified a Lee 32-20 Collet crimp die to crimp the heel. Well..I squished them into hourglass shaped heels and made them undersized a bunch. live and learn sometimes

"if it was easy we'd let women do it" don't tell my wife I said that!

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