Expensive Story

[montec]

A while ago I posted of a rifle that could not hold POI. This problem gradually crept in over the last 3 yrs.The rifle was a Rem 700 VSSF in 22-250. The handload was 36 gr Varget behind a 50 gr Ballistic Tip. This combo would shoot a ragged hole under 1/4" at 100 yds.Scope is a Baush & Lomb Elite 4000 6-24.From day to day,if not hour to hour, it could not hold POI.After lots of advice,I glass bedded the action. This helped a bit but the POI was still moving.I then sent the rifle out for action truing and a new barrel. Got it back and still the same problem. Now the process of elimination. My 7MM Mag has a Bushnell Elite 4200 6-24 so I switched scopes, same problem.
Next, bases and rings, 3 different combos and still the same problem. What's going on??? I was at wits end before I broke down and tried factory ammo, that gagged me to put factory thru a costom rifle, talk about a cumquat in the Garden of Eden.
Well, it grouped,let the rifle sit for an hour, it shot another group on top of the first.AAAAHHHH, maybe it doesn't like BT's anymore.Went out and bought some Hornady Varmint 55 gr SP's and now I got my tack driver back and the POI stays put. That 55 grainer is a smaller sized bullet as compared to the 50 gr BT. I finally come to the conclusion that it was a rate of twist issue. I tried different charge weights, seating depths,etc to try and get that thing to shoot and spent a lot of money doing so.
My question is how could a certain rate of twist no longer stablize a bullet it did for years

 

[montec]

Thanks for the input Dave. I have never heard of that calculator.What would a good stability factor be
since I was thinking of dropping down to the 50gr Hornady SP. What/where is the formula or is this calculator a physical thing?

 

[BoydAllen]

Do you have any then and now velocity numbers with the load that stopped working? You are making me feel better about my Savage .220 Swift coming with a 12" twist barrel Thanks for sharing your experience.

 

[bheadboy]

Montec, i have had the problem in the past 50 yrs of reloading, - the bullet mfg, ware out forming dies fast as the make millions of bullets, then from time to time the ojive, bearing surface, is change for what ever reason.

the result is the "same" bullet, has a different shape and shoots different.

Bob

 

[RGRobinett]

Just go to JBM Ballistics home page. On the left there is a link to calculators. The stability calculator is the bottom one. Randy Robinette tells me that ideally you want a stability factor in the area of 1.3 to 1.5 if I recall correctly. The calculator uses colors in addition to the numerical value.

There's also a link called "Lengths". That page has the length of most of the bullets you're likely to run into which you need for the stability calculator.

http://www.jbmballistics.com/ballistics/ballistics.shtml

Best results should come via a bullet/twist combination which results in Sg (gyroscopic stability factor) between 1.4 and 1.9. While combination outside this 'window' may, in some instances, work well enough, don't count on it . . . except, that with HIGH quality bullets, it doesn't hurt [much] to spin the bullets 'too fast' - especially for hunting applications, where a few one hundredths (0.01s) won't make the recipient any deader.

Oh, and within 'normal' velocity ranges, for center-fire cartridges, don't count on a few tenths of a grain of powder - or, even several grains - to alter [observable] Sg numbers.

Keep 'em ON the X! RG

 

[jonbearman]

I have a 22-250 vs remington and according to the calculator,almost nothing that shoots good in my barrel wont work? This is really weird as I get 1/2 minute or less in my rifle. Why do so many companies use the 1:14 twist in the 22-250?

 

[DCRYDER]

I think Boyd is on the right track here. I know that my Shilen 280AI lost velocity during break in. First few shots through it i was getting 2980fps with 59 grains of n165, 59.5 gr showed slight pressure signs. After break in and about 150 shots that same load chronoed at 2920fps. I worked my way back up to 2980fps and it took 61 grains of powder and still no pressure signs. I guess the smoother the barrel the less pressure and velocity is made. I haven't shot any 50gr Btips in a 14 twist but i know mine always loved the 50gr Blitzkings.

 

[pintopete]

Both of my Rem 700's with 14 twist barrels would not stabilize 60 gr bullets at all and are better with 55's (1 1/4") but will do much better with 50's (5/8" with 50gr Sierra SP). I have not yet tried all 50's or 40's either. As far as your troubleshooting is concerned, I would say that you can assume you have a good barrel and good bedding. It seems as though you have tried to hash out your scope and mounts. So I would assume all that is good. The first thing I would do is load up about 10 of your previous favorite load and chrony it. Write down all the load details including distance from rifling (ie .020). I love MS Excel for that. After that, I would try some pretty standard known good combinations like Varget or H4895 powder and some Hornady V-Max 50 gr and Sierra 53 gr 1400 Matchkings and Winchester Std LR primers. Flat base bullets may be easier than boat tails. Pick through your brass, sort it, prep it weigh it etc. I would stick with a fairly modest load, not one on the ragged edge and use your chronograph so that you know where you are at. Some say that 22/250's like loads that are close to max but for your trobleshooting I would start more conservatively. The best way to find the source is to change only one thing at a time. Are you shooting from a bench or prone? Is the barrel free floated? Did you stick with the heavy barrel? Is your trigger good, not necessarily light but is it smooth and consistent? Try to stick with changing only one thing at a time. Try to keep your cheek weld, eye relief, trigger stroke etc as consistent as possible. It could be that you have two or more contributing factors. Sorry if I have stated the obvious. Good luck, Peter.

 

[montec]

Thanks Pete. To answer some of your questions,I am shooting off a rock solid bench using sandbags.The barrel is free floated with approx.020 between fore end and barrel,action is glass beddedand yes I stuck with a heavy barrel. The trigger has always been smooth and being a former archery champ, I understand completely about a clean breaking trigger.
The JMB Stability Calculator was very interesting so I got to checking out bullet lengths and I may try the Speer 50 gr Sptzer SP. It has a length of .620 and the stability factor was over 1.5 for a load of 3700 fps. I don't want to go too light since I want to have enough thump for those 500 yd hogs.

 

[pintopete]

Montec, Like you I had a bit of trouble getting my 700V in 22/250 to shoot well this summer. The rifle got a new barrel to replace the old burnt up factory barrel. I was hoping that I could use some nice 60gr HP bullets and some 55's. The 60's were all over the map. I then tried some Sierra 55 and Hornady 55 SP bullets and the groups started to come together. The Sierra and Hornady 55's print in different spots but both seem to produce about 1 1/4" groups. Then I switched to 50 gr Sierra #1330 SP bullets and got one 5/8" 5 shot group. I am hoping that when I get back to it that I will have as good results or perhaps better. I have not yet been able to find any Hornady #2245 50 gr SP bullets but I am hopeful that they will work as well. I have some 40's on hand but have not gotten to that either. I was using Federal prepped brass with CCI std primers, 36.0gr RE-15 and the Sierra #1330 50 gr bullets seated .020" off the rifling. Some of these components were just used because that is what I had on hand. Unfortunately my chrony batteries were dead so I do not know what velocity they were. I shoot prone with a Harris bipod and a bag because I have no bench and also it may be the way I will shoot in the field. My trigger was a hitchy diaster so I worked on that as well. I put a "Favorite Loads" post over on the Saubier site and we are also lucky that there is the new article here on the 22/250. Good luck, Peter.

 

[BoydAllen]

It has been a long time, but at one time that I had a heavy barreled Ruger model 77 (the old tang safety model) that came to me through a trade. I was under the impression that it had a 14" twist barrel. The throat was too long for me to touch the rifling with 55 grain bullets, so I bought some Berger 60s and 65s, both FBHP designs. I worked up loads with H414 and ended up about a grain and a half over what the manual showed as maximum loads, for my best accuracy, and no pressure problems. They shot fine, under 1/2".

Several years later, I submitted a short piece to Precision Shooting asking why some barrels (I was primarily referring to factory barrels.) don't like BT bullets. I wrote it after an experience with a friend's FN .270 that showed a marked preference for FB bullets. That little article got a lot of responses in subsequent articles by others, in the same magazine. While there were various theories as to why this was, all who responded were familiar with the phenomenon.