Neck Space question

[45&30-30]

I have assembled 8 different loads with 4 powders and will be testing soon. Does anyone know what the minimum amount of neck space necessary for a loaded cartridge? I am shooting a Marlin 336, 311413 GC boolits sized .312. Fired case neck outside neck diameters range from .332 to .333 and the cartridges necks loaded are at .332. I feel a slight resistence when the case goes in to the chamber. It is definately not due to bullet length. I am .005 off the lands.

Should I cast the chamber to make sure where its at? Will I be a candidate for a blow up if the necks aren't expanding much to release the bullet? How tight can they be?

Thank you for any help on this.

[knifemaker]

If you are sure it is neck case dia. causing the resistance, you can cause higher pressure upon firing. This could lead to problems if you are at max loads. Are you also sure that you set the case shoulder back enought that it is not causing the slight resistance?
If the neck dia. is the problem and you must have the bullet at .312 dia for best accuracy, you should look into getting a case neck reamer to thin the walls of the case neck several thousands to correct any problems.

[Houndog]

Lyman lists the MAXIMUM LOADED outside neck diameter as .332 for the 30-30. a .332-.333 neck on a fired round puts it right where it supposed to be. Measure your LOADED round and see where you are. That's the one that REALLY matters. You should also recheck your die setup and make sure you are sizing the case enough. All lever actions are notorious for their weak camming a round into battery. The only way to really know what your finished chamber's neck size is is to do a chamber casting with Cerrosafe and measure it. I setup my benchrest rifles with a neck clearance of .002, but I'd consider something along the lines of .004-.006 as a MINIMUM on a field rifle.

[largom]

As per your post: fired case necks = .332, loaded case necks = .332

Do to brass springback you probably have .001 clearance for neck expansion. That would be 1/2 thousand per side, too tight IMO. If you measure your case neck thickness you will find a lot of variance. Unless you turn the case necks to a uniform thickness you will, sooner or later, get a case on the thick side. That loaded round could measure .333 or .334 and you still might chamber it. Upon firing pressures would go thru the roof.

To be on the safe side you need to do ONE of three things. 1.= Reduce the Dia. of your boolit. 2.= Ream the inside Dia. of the case necks. 3.= Turn the outside Dia. of the case necks.

Turning the outside of the case necks has the advantage of giving you uniform neck thickness which gives uniform neck tension and uniform crimp, if cases are uniform in length.

Larry

[.30/30 Guy]

Try a different lot or manufacture of brass. The neck thickness differs between lots and manufactures.

I need to turn the necks for Federal, but not Winchester brass when using 0.312 boolits.

The Federal brass also seem to have a thicker neck thickness at the shoulder than at the end of the case.

Get a good outside turning tool such as the K&M.

[Larry Gibson]

I will throw this information out as to my experiences and experiments on this subject, it still remains your choice to do as you see fit.

I have for many years used over sized bullets, both cast and jacketed, in several cartridges. In many instances this has resulted in a tight fit as described. The common thought is the tight fit "will increase pressures". The question is; does it really? In my tests and experiments measuring pressures via an Oehler M43 I have found no indication that it is the "tight fit" of the loaded cartridge neck into the chamber that increases preasures. Caveat; If the case neck is too long and is crimped solidly into the bullet by the front of the chamber throat then pressures do increase. However, we are not talking of that situation here. Here we are talking of the diameter of the neck being a tight fit to the diameter of the chamber neck.

Let us consider bench rest shooters (those shooting J bullets); they have very tight necks in the chambers so they can turn the case necks to give a tight slip fit just as we are discussing. They load their BR cartridges to some pretty high psi's, higher than most cast bullet loads. However, they are shooting J bullets of groove diameter. In this case we are shooting a softer cast bullet of larger than groove diameter.

I recently ran a test as part of the RPM tests comparing the accuracy of 311466 bullets sized .308, .309, .310, .311, .312 and .314. The .314 bullet in the .308W case neck created exactly the same situation in the match chamber of the Palma rifle as is the subject of this thread. The results of pressure testing a 10 shot string of each size of 311466 showed no increase in peak pressure. The load was producing 2500+ fps so it was not a mild load. There was 1,200 psi difference between the lowest psi and the highest. Though the .308 sized bullet did produce the lowest psi it was not the .314 bullet tha produced the highest psi. There was no correlation between the size of the bullet and the increase in psi. I will also add that the 1,400 psi variation is about the same average variation between test strings of identical cast bullet loads. Thus the variation of each different sized bullet was within the mean average of the extreme spread of the peak pressure.

What was not was the correlation between the size of the cast bullet and the sharper rise of the pressure curve as the size of the bullet increased. This was a consistent increase in rise and did not "spike" with the .314 bullet. Based on a large number of previous tests this indicates simply the early increase in pressure due to throat sizing down the bullet. In any case the peak pressures remained consistent regardless of the diameter of the bullet as long as the bullet was at least the diameter of the groove depth.

Bottom line; As long as the case mouth does not get crimped during chambering I would shoot them especially since these are "worked up loads". The bullet should be very well supported and little obturation should occur in the case neck and thus accuracy may be about as good as it will get.

Larry Gibson

[StarMetal]

I would be careful with what Larry said as long as they don't crimp the case mouth when chambered just shoot them. When I was working up HV loads for my 6.5x54MS I had some case necks that were very close to max diameter for the chamber and I locked my bolt up. I use military cases so I can get the thicker necks. So be very very careful with too long a case and case neck that are either tight or too close to that maximum.

Joe

[45&30-30]

Excellent information, thank you all very much. I had not considered the possibility of the case neck being crimped by the rifling. I used a trim to length of 2.0295 for all cases and though I feel I am short enough, I could have a short chamber. I will find out for sure with the chamber casting. I will also check the die for shoulder set back and thank you for the information on neck sizes and brass spring back. Will also look at neck trimer or different brass once I isolate the problem(s).


In any cast the peak pressures remained consistent regardless of the diameter of the bullet as long as the bullet was at least the diameter of the groove depth.

Larry, thank you for sharing your test information. I had a question on the sentence above. This may be common sense but I want to know for sure. Does this mean that if you were to use a .306 or .307 bullet and it didn't immediately obturate then pressure would be lower and erratic because of gas blow-by?

Thank you all again.

[Larry Gibson]

45&30-30

"Larry, thank you for sharing your test information. I had a question on the sentence above. This may be common sense but I want to know for sure. Does this mean that if you were to use a .306 or .307 bullet and it didn't immediately obturate then pressure would be lower and erratic because of gas blow-by?"

That is correct, the groove depth of the test rifle is actually .309. The .308 sized bullets peak pressure was indeed the lowest and also it had a longer time under the pressure curve indicating the pressure was not rising consistently. The actual pressure graphs were also not as uniform as those with the .309-.314 bullets. Those bullets obviously sealed the throat and there was no indication of gas blow by with them. Additionally the .308 sized bullets gave the worst accuracy. My test results with other bullets and/or cartridges confirms that undersize cast bullets do not have as consistent internal ballistics as do those of at or slightly larger diameter cast bullets. Initial gas blow by seems the logical reason. Hope that answers your question. Be glad to further elaberate if not.

Larry Gibson

[45&30-30]

Thank you Larry, that does answer my question. Your use of the words "consistent internal ballistics" paints a good picture and helped me understand more of what is going on in the barrel.

Best 45&30-30

[JSnover]

You guys rock! I just got interested in my chamber/cartridge neck dimensions last week and here comes a thread that answers all my questions.

[45&30-30]

I just completed my first chamber cast with CerroSafe. I was reluctant to do it because of several reports here of stuck castings in the chamber requiring time comsuming methods to free the alloy from the chamber. Using a Lee lead laddle, I used a propane torch slowly passing it under the CS until it slowly dripped in to the laddle. The chamber was spotless, then I used Hoppes oil on a jag with patch and lightly lubricated the chamber. A jag was placed in the barrel from the muzzle allowing 1/3" of rifling to be cast with the chamber. Using a 30-06 casing with the base cut off as a funnel. A hair dryer was used for about ten minutes to heat the chamber, barrel and brass funnel. I heated the ladle of CS by passing the propane torch under it for several minutes until it started to enter it's liquid state. I allowed the heat from the laddle to continue to heat the alloy and gave a few more passes under it until I was sure it was all in solution. I did this slowly so as not to over heat the alloy. I poured it in the chamber and waited for the laddle, which was half full, to solidify. This took a little over a minute. Then checked the chamber casting to ensure it was solid. I gave a slight tap on the cleaning rod handle and the casting popped right out. I waited an hour and took my measurements.

After one hour the lands measured at .3095 and the groove at .305, this seemed a little large to me. But may explain why J-Boolits have not been very accurate in this rifle. It was bought new 2 years ago. The neck measured at .333. Comparing the casting to my cartridges that were difficult to chamber with the ones that were not, I noticed the difficult cartridges did not have a sharp shoulder line around them and tended to have more of a rounded appearence. I have narrowed the problem down to the fact that some of my casings did not get the full benefit of resizing and are causing the problem. From what I am getting from this is I need to ensure I am getting a full sizing on my cases by adjusting the dies down slightly. The chambers neck length is plenty long and I do not have the problem of the rifling crimping my cases further. I feel I should be safe in this area. If the .312 bullet shoots exceptionaly I will consider staying with the size but neck turning. First I will see if .311 bullets allow the same accuracy to save me one step by reducing the neck size. Thank you all for your great contributions. Eventually if they are worth adding here I will share the results. I am using 2400, h335,h332 and IMR 4831.

I would really like to see the 2400 prove to be the hands down winner as it is my favorite powder. Are their other fillers I can use instead of the dacron that would be easier to meter out?

[StarMetal]

I just completed my first chamber cast with CerroSafe. I was reluctant to do it because of several reports here of stuck castings in the chamber requiring time comsuming methods to free the alloy from the chamber. Using a Lee lead laddle, I used a propane torch slowly passing it under the CS until it slowly dripped in to the laddle. The chamber was spotless, then I used Hoppes oil on a jag with patch and lightly lubricated the chamber. A jag was placed in the barrel from the muzzle allowing 1/3" of rifling to be cast with the chamber. Using a 30-06 casing with the base cut off as a funnel. A hair dryer was used for about ten minutes to heat the chamber, barrel and brass funnel. I heated the ladle of CS by passing the propane torch under it for several minutes until it started to enter it's liquid state. I allowed the heat from the laddle to continue to heat the alloy and gave a few more passes under it until I was sure it was all in solution. I did this slowly so as not to over heat the alloy. I poured it in the chamber and waited for the laddle, which was half full, to solidify. This took a little over a minute. Then checked the chamber casting to ensure it was solid. I gave a slight tap on the cleaning rod handle and the casting popped right out. I waited an hour and took my measurements.

After one hour the lands measured at .3095 and the groove at .305, this seemed a little large to me. But may explain why J-Boolits have not been very accurate in this rifle. It was bought new 2 years ago. The neck measured at .333. Comparing the casting to my cartridges that were difficult to chamber with the ones that were not, I noticed the difficult cartridges did not have a sharp shoulder line around them and tended to have more of a rounded appearence. I have narrowed the problem down to the fact that some of my casings did not get the full benefit of resizing and are causing the problem. From what I am getting from this is I need to ensure I am getting a full sizing on my cases by adjusting the dies down slightly. The chambers neck length is plenty long and I do not have the problem of the rifling crimping my cases further. I feel I should be safe in this area. If the .312 bullet shoots exceptionaly I will consider staying with the size but neck turning. First I will see if .311 bullets allow the same accuracy to save me one step by reducing the neck size. Thank you all for your great contributions. Eventually if they are worth adding here I will share the results. I am using 2400, h335,h332 and IMR 4831.

I would really like to see the 2400 prove to be the hands down winner as it is my favorite powder. Are their other fillers I can use instead of the dacron that would be easier to meter out?

Not to nick pick, but I do believe you have the land (which is the bore diameter) size and groove size reversed.

Joe

[45&30-30]

You got that right Joe, that would be a strange barrel indeed. :confused: Groove .3095 and lands .305. Thank you.

[JSnover]

I did my 45-70 neck slug a little different; Took a Lee .54 REAL boolit cast from pure lead and used my case sizing die with the decapper removed to swage it down till the front band measured .490" (dribble a little transmission fluid into the die to make things easier) Drove it into the chamber until 'bottomed out.' Measured the front band again: .486"