Im feeling like a _______ trying to figure twist rate.

[crackerjack57]

Hello Gentlemen. Im trying to figure out this twist rate thing for my Russian SKS and Norinco 7.62x39 rifles. i am shooting the lee 155 and 160 gn cast boolits made for this rifle. I am having good results in the bolt action norinco using the 155 grainers at about 2-2 1/2" at 100 y and if i clip the tip off giving me a flat nose and about 146 grain even better at 1 3/4" at 100 y. by the way, gas checked and sized to .312 wheel weights bn of 15. 14 1/2 gn of alliant 2400.

when i try this load in the sks and anywhere up to 16 1/2 gn of the 2400 i get 4" AT ONLY 50 Y. Im not quite ready to give up yet. so I did a little looking on the net and trying to figure the twist rate to bullet stability. according to the formula i should have a twist rate of 1:16 not 1:9.5 like the sks is. according to the trist rate formula i should be shooting a bullet that is roughly 1.45" long to match the barrel twist rate. well for this sks, that would be like lobbing a cannon ball from a sling shot. Im not sure of the twist rate of the bolt action norinco but it has got to be around there somewhere im thinking.

Just a little clarity is all.

Thanx

[44man]

Nothing you read will give it to you. I will forever never believe it is bullet length but it is drive area length. Some long bullets do not have much drive length touching rifling. Some short ones have a lot.
Every single formula will give a slower rate then what you really need.
Greenhill is the worst, it was made for cannons. Some alter the formula to suit what they shoot but it fails for other guns.
Personally, I want a faster twist.

[PS Paul]

To elaborate on 44man's post, many rifle boolit mold designs have very little driving band touching the rifling. Some claim the bore-riding design is best, but it ain't always so. First things first (I am not exactly sure what the Lee design is and cannot check right now), at .312, can we presume you know the dimensions of your rifle? Could be too small OR not exactly fittin' the chamber? THAT is where I would start: figuring out the fit and THEN fine-tuning the load and boolit....

Don' know if this helps or not? Maybe too basic and elementary?

[crackerjack57]

I did some more looking at the twist rate of my norinco and its a 1:9.5 aswell. not that I can change my twist rate but just for my own information I was wondering if my SKS might like a different bullet as it shoots like **** with any given combination but best with my 180 grainer paper patched .308 cast bullets with unique powder. only problem is they're too slow to use for hunting. not enough jam for deer.

[crackerjack57]

I slugged my barrel and it comes out to .311. as for the lee cast mold, its the one designed for the sks. same bullet shape as the factory loads is what lee was trying to get but heavier because of being made out of lead. seating boollit back from touching rifling about .002-.003``

[runfiverun]

that chrome lined barrel can't be helping the situation any.

[crackerjack57]

Nope.... No chrome. Its a 1950 model. no chrome. All steel and in mint shape. Im a junior gunsmith so I`ve got lots to learn but this thing is stumping me. I even went right down to remove everything from the barrel. bayonnet, plug up gas chamber and remove gas tube, basically free float the barrel so the only variable is the barrel itself and just plain crappy results. even crowned the barrel. just plain crappy results. Im almost wondering if I should make my own mold that would be set up for paper patching thats longer, more area touching the lands with a rounded nose. hopefully around the 160 gn mark.

[subsonic]

Twist is just one variable. I would say that it is not the twist that is your problem if you have another rifle with the same twist that is working just fine.

What rifle is a Norinco 7.62x39 bolt action??

[44MAG#1]

I feel compelled to make a statement on the word "RETARD"
I know that it was meant in a comical way but, that is a word that to some, who may have a son or daughter that is retarded, may be hurtful.
My dad had a retarded sister who couldn't help the way she was. she never hurt anyone or even caused any problems.
She would sit and play with dolls and would keep to herself mostly.
Some mildly retarded people will be hired for meanial jobs such as table cleaners and such at McDonalds and other jobs at different places.
Someone on here may have a child or a close family member that is in that situation and I for one wouldn't want to offend anyone by using the word "RETARD" in even a joking way.
I am not saying we should be politically correct all the time, but, there is a line that we should not cross by being disrespectful just because we can.

I hope everyone understands what I am trying to get across.

[Chilmonty]

How about "Barrel Detection Challenged"?

Just kidding, don't Taze Me!

[crackerjack57]

Oh! Im sorry 44mag. there was no offense intended on my part and if I offended you or anyone else, I apologize. I was just looking at my math skills and thinking that after doing the calculation with the bullet used i should have a twist rate of about 1:14 not the regular 1:9.5 like they are all made to. I was thinking that my math skills were going down so far that if they entered me into the tv show ``are you smarter than a 5th grader`` i would defiantly loose!

[crackerjack57]

In an hour or two I will post some target results and I will also see what I have for pix of the norinco.

[joesig]

that chrome lined barrel can't be helping the situation any.

Please enlighten me why that would be the case? I would think chrome would be less susceptible to leading and an overall benefit.

[crackerjack57]

I have heard of great results with a chrome barrel and the lead would probably be less. i cant comment as I have never had one. However, I have heard of some that have ran quite a few shots through a chromed barrel and if the chrome lining starts to peel off your barrel is junk. I guess that for one, am working in the steel industry and steel has never done me wrong. 2, have seen what can happen when chrome starts peeling off of steel. look at some old cars that had chrome over steel. look nice at the start but when it starts to peel is a mess. imagine a bullet passing over an area where it might start to peel off of. 3, just old fashioned. I figure if some of the rifles out there are over 100 years old and can still ``shoot yer eye out`` thats good enough for me. as for both of my rifles, all steel bore and i am having no issues at all with leading.

[crackerjack57]

Here are pix of my sks and norinco. also target results.

[crackerjack57]

the last picture is after dialing in the scope and its 3 shots at 100y. the modified 146 gn lee cast with gc and 14.5 gn of 2400 running at 1850 fps. the second last pix is a 5 shot group at 50 y. it is actually upside down. sorry. 5 shots using 7.5 gn unique and the 146 gn modified lee cast with gc. third last is 5 shots. 1 is a flyer and the other 4 together. 7 gns unique with the modified 146 gn gas checked cast. the picture with the multiple targets is what i was using to work up some 180 gn loads. poor results for the most part. all were 5 shot groups. with exception to the bottom left which i have posted as a single pix, the only other one that was any good was the middle right. it was running 146 gn lee modified with 14.5 gn of alliant 2400 gc. with exception to the last picture which was scope adjusted to the 100 y poi all others are aimed at the center and that was the results. some 5 shot groups only had 1 hit the intended target.

[crackerjack57]

I forgot to mention...... all the target results are using the norinco. the sks just does about 5" groups at 100 y and they could be high, low, left or right. It has a mind of its own.

[rond]

Is your scope base touching the spring cover on the SKS? If so, it is taking a hit each time you shoot, could affect the zero.

[crackerjack57]

Nope. lots of clearance.

[tom357mag]

I feel compelled to make a statement on the word "RETARD"
I know that it was meant in a comical way but, that is a word that to some, who may have a son or daughter that is retarded, may be hurtful.
My dad had a retarded sister who couldn't help the way she was. she never hurt anyone or even caused any problems.
She would sit and play with dolls and would keep to herself mostly.
Some mildly retarded people will be hired for meanial jobs such as table cleaners and such at McDonalds and other jobs at different places.
Someone on here may have a child or a close family member that is in that situation and I for one wouldn't want to offend anyone by using the word "RETARD" in even a joking way.
I am not saying we should be politically correct all the time, but, there is a line that we should not cross by being disrespectful just because we can.

I hope everyone understands what I am trying to get across.

Thank you 44