Winchester Model 70 with a long throat

W

William T. Watts

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Fellows I have a Winchester model 70 featherweight built about 2006 + or -, this action was used in a multitude of calibers from 22/250 thru .308, a spacer is attached to the rear of the magazine to prevent an over length round from function thru the magazine. I thought it might be possible to increase the OAL of a loaded round from the factory established 2.350" to whatever the throat & magazine would allow. I found that the throat would allow chambering a dummy round of 2.450". I found the magazine length was 2.440" and decided to assemble some dummy rounds of 2.425" and run them thru the magazine to ensure they would feed/chamber and eject properly (they did). I was shocked, never ran into this before, the max load for this round is 36.2 grs of IMR4064 with a 55gr Sierra SP bullet. I'm toying with the idea of exceeding the max load but have never done so, interesting dilemma, I guess this means I need to break out the chrony. On a side note I have some Remington factory ammo that I checked a couple of fired cases and found there was zero expansion over what would be the expansion ring ( the part of the cartridge that isn't supported by the chamber). Looked at some of my cases I had loaded and found there was zero expansion there also. I have some virgin 22/250 cases I will load and fire and check them also. My personal load for this rifle is 35.3 gr of IMR4064 & 55gr Sierra SP R-P cases CCI LR primer OAL 3.250 1" groups off of sand bags. At my age (72) soon to be 73 that's about as good as I can do any more.. I guess we do the things we do because we can!! Non the less interesting!!

Fellows If you don't have the training and experience I wouldn't try this one, leave it alone, I have more than 42 years loading ammunition and am a school trained Gunsmith TSJC! For now I am recovering from a torn rotator cuff injury and surgery and will pursue this further when my shoulder will allow. William
 
WTW - what are you going for .... accuracy .... Speedy Gonzalez?? If accuracy just play with it until it is a better load than you are a shooter.
 
I think he's going for amusement.

Compare the original load and the longer one on the same chronograph on the same day. I even alternate between loads of the same powder doing this sort of comparison and record the individual velocities and segregate the odd and even ones later to do the stats later in Excel instead of letting the chronograph do them. My idea is to balance the influence of barrel temperature and fouling.

The trick is that peak pressure can go up or down as you move the bullet closer to the lands. If it goes up, your velocity will go up, but your peak pressure will go up even more. The square of velocity (actually, KE) is proportional to the average pressure in the bore, but the peak changes more than the average because the muzzle pressure only changes nearly directly with charge weight. So, if velocity increases, merely reducing charge until it matches the previous number does not actually bring peak pressure all the way down to a match. Reducing the charge has cost you late barrel acceleration by having less total gas generated by the powder, and velocity is maintained by making that up with higher peak pressure.

The reverse is also true. If your velocity decreased when you moved the bullet out (quite possible if you still aren't too close to the lands), then bringing the charge weight up to a velocity match won't actually bring peak pressure all the way up to a match, meaning you can then go for a charge that produces slightly higher velocity.

And where dose accuracy fall in all this? Well, if your accuracy is based on meeting a certain barrel time so your bullet exits the barrel at the same point of phase in the muzzle swing from harmonic vibration, you will find that adjusting the charge to compensate for change in seating depth, constant barrel time requires a charge adjustment that is in between the charge change that produces the same velocity and a charge change that produces the same peak pressure.

Not to tease, but I have a formula that seems to be working pretty well, according to QuickLOAD, at finding a constant barrel time charge adjusttment based on expansion ratio and how much change in velocity a fixed charge produces with a change in seating depth. I don't have it organized in a presentable way yet, but after tax season ends, I'll try to put something up on the subject along with other elements of load development. With published measured pressure vs. powder charge, the necessary exponents can be derived. I'll try to put it in Excel for easy data input. Until then, the best route is to get QuickLOAD, adjust powder burn rate and case capacity until you can make the program predict your measured results fairly closely. Then you can find what charge weight produces the same barrel time after a seating depth adjustment and go with that.
 
Unclenick I'll let you know the results when I know!

I'm trying to reduce the distance the bullet has to travel before engaging the rifling and maybe reduce group size, I assume velocity will go down when I increase OAL. I'm going to start with the same charge of 35.3grs which is what I use now, I'm well under the max charge and compare velocity and accuracy. What I expect is velocity will go down and I will increase the charge until it equals velocity of the shorter OAL and hopefully smaller groups. I'm not trying to duplicate the velocity of a .220 Swift plus I'm doing it because I can without damaging the rifle or myself. In my rifle with the long jump to the rifling this load is a low pressure load. There isn't any expansion I mean zero expansion over what should be the pressure ring where the case is unsupported by the chamber. Another point factory rounds fired thru my rifle there is zero expansion where the case is unsupported by the chamber. This isn't an experiment in the truest sense because I think there are predictable results. Velocity will equal factory velocity or slightly higher with equal to or smaller group size with a small increase in powder charge. If the groups don't shrink I will change nothing.. Until my shoulder improves enough from surgery to shoot and use my chrony I'm not doing any shooting.. If nothing else it gives me an excuse to go the range and have some fun! William
 
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Anything that reduces bullet deformation upon its entry into the rifling improves accuracy.

That said, here's some issues.....

Bullets seated out far enough to touch the rifling are well centered in the rifling's origin. So they start out pretty straight; assuming they're straight on the case axis, too.

Depending on the angle of the rifling at the throat and the shape of the bullet's ogive, starting out against the rifling may not work well and for some reason, it deforms the bullet more than if it had a short running start into the rifling.

Accuracy differences are small across all sorts of combinations. It takes repeatable performance of shooter and rifle to see the difference in ammo types. And one has to shoot enough shots per test group for them to be significant statistically. One may not be willing to shoot 20 to 30 shot test groups to get up in the 90% plus range of a load's accuracy being meaningful.

One thing's for sure; if you shoot several groups with the same load and they're not within 10% in size (extreme spread) of each other, none of them have enough shots in them to represent the real accuracy of that load as one shoots it.

Ever wonder why there's hundreds (thousands?) of favorite load recipes and bullet jump distances for a given cartridge's bullet across many rifles?
 
Long throat M-70

:confused:WTW;.......Magazine length= [2].440"......Throat allows chambering [2].450"......Fully cycles dummy rounds of [2].445".......Your personal load is; [3].250"...What am I missing here?

Bart, Flash, Unclenick; Is there more to this than what I'm seeing? WTW's personal load is a FULL .9" over factory 2.350" OAL. TYPO?
WILL.
 
Sounds like you might have the option to go with a lower pressure powder and increase the charge weight to take advantage of the extra case capacity. I like how Hodgdon publishes pressure data with their powders. A different powder choice my not put you in an over-pressure situation at all and let you minimize bullet jump with a full case.
 
On a side note I have some Remington factory ammo that I checked a couple of fired cases and found there was zero expansion over what would be the expansion ring ( the part of the cartridge that isn't supported by the chamber). Looked at some of my cases I had loaded and found there was zero expansion there also. I have some virgin 22/250 cases I will load and fire and check them also. My personal load for this rifle is 35.3 gr of IMR4064 & 55gr Sierra SP R-P cases CCI LR primer OAL 3.250 1" groups off of sand bags.
Click to expand...

That is what I would do, I would start with factory, I would measure before and again after. I would then use the once fired cases for test cases. If his case heads are not crushing/expanding over factory loadings there is a chance he is using thin cases or a loose barrel, 'OR' has a long chamber from the shoulder to the bolt face.

Internet forums will say he has cases with head space problems. Cases do not have head space according to SAAMI, I adjust the length of the case to off set the length of the chamber.

Ever wonder why there's hundreds (thousands?) of favorite load recipes and bullet jump distances for a given cartridge's bullet across many rifles?
Click to expand...

No, I don't. I ask, what does the rifle like?


F. Guffey
 
And, I would want to know how long the throat is. I would drill the primer pocket/flash hole out to a diameter that would accommodate a cleaning rod. I would neck size a fired case to get all the bullet hold I can get then seat a bullet, remove the bolt then use a cleaning rod to push the bullet out to the lands.

I would not jam the bullet into the lands, I want the bullet to come out with the case. After removing the test case use it as a transfer, use the transfer to adjust the seating die to zero on the seated bullet. Zeroing the seating stem allows the reloader to seat the bullet off the lands.

Save the transfer, saving the transfer prevents the reloader from starting over every day.

F. Guffey
 
Winchester model 70 Featherweight 22/250

Guffys last post yesterday is a doable solution for precise measurement for OAL, what I hope for is to improve on the 1" group size that the rifle produces now. To Unclenick still trying to figure your amusement comment, to me anytime I load or talk about loading ammunition it's serious and has my full attention.. To the rifle, it's somewhat rare, I've never heard nor seen another Winchester Model 70 Featherweight 22/250 from this time period (some time after 2002), the barrel may be to light to produce good accuracy. The 1-14 twist barrel will not produce the group size I desire with the Sierra (#1360) 55gr spitzer, the semi point Sierra (#1350 .041" shorter) may offer the best option for the smaller group I'm looking for. What I want to do is reduce bullet travel as much as possible within the parameters I must work with plus the long throat this barrel has and long magazine length 2.440". I begin with the length of the loaded ammo 2.350" per Sierra's max length, I have found rounds 2.432" long will function thru the magazine and chamber fine will have approx .016" travel before engaging the rifling. I plan to use Guffy's method to determine exactly how far the bullet has to travel before engaging the rifling before I start to assemble ammunition. I have several more months of therapy (rehab) my left shoulder (torn rotator cuff) that was repaired this past Dec 31. I have not shot any rifle since and don't plan to until the surgeon tells me it's O.K. to proceed. This is on my to do list just not now!! I do not intend to post anything else until I am able to load and shoot the Featherweight Winchester which will be sometime this fall.. William
 
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