Wild POI shifts between different ammo?

R

rms65

New member
Hi guys, I'm new to this forum and hope I'm posting this in the right one. I know different brand cartridges and loads commonly produce different points of impact but I have owned a couple of rifles that differences can be so drastic I'm left to sight the gun in for one type and stuck using one bullet. My latest dilemma is with a Savage B17F (sporter barreled 17hmr) that has a 6" spread between different types of bullets at 50yds. From the lowest printing ammo type the groups for each different type climb and go right. Basically resulting in groups running from 8:00 to 2:00. I've never had such wide variance between ammo especially @ 50 yards. So the question is why does this happen. I know the answer is a technical one that's why I chose this message board
Thanks
 
I took two 300 Win Mags to the range, one shot one hole groups, the other did not shoot groups; it shot patterns like a shot gun with the same ammo.

I built a 270 Winchester, I took 120 rounds of 12 different loads using different case head stamps and different bullets. The 270 produced magnificent groups without a flyer. Some of the groups moved but none of them opened up.

I wanted to know what the rifle liked, it liked everything.

I bid on and won the ugliest rifle contest, my interest was 'the sum of the parts' but first I wanted to know what the builder was thinking. Again I loaded 12 different loads w3ith 12 different head stamps and bullets, I used different bullets. The groups did not open up and there were no flyers, some of the groups moved around and some of the groups used the same hole but there was nothing I could do to improve on the accuracy so I left-er the way I won-er.

My thinking? No one could bu7ild a rifle 'that ugly' without knowing what he was doing.

Is there a moral to the story? If the rifle shoots like a shotgun there is not much the shooter can do by changing ammo.

Back to the 300 Win MAg that shot patterns, I sent it back to Winchester, before it got back to Winchester their warranty man in the DFW area had a go at it. I told him the chamber was too long from the shoulder to the bolt face and the chamber was too large in diameter 'AND!' the chamber was ugly. SO? He polished, reamed and honed the chamber, when finished the chamber was still to long, too large in diameter and just plain ugly. So I asked him which remedy made the chamber shorter, or smaller in diameter and what process removed the 'ugly'?

He responded with "the chamber is still to long. too large in diameter and ugly?" He claimed it was that way when I brought the rifle to him:confused: and then? It did not get better.

F. Guffey
 
Rimfire rounds are notorious for doing this. The 17HMR isn't an exception. First off, you didn't say what bullets you were using and what you changed to. The 17HMR comes in 15, 17, and 20 grains bullet weight. Changing bullet weights will make a big difference in POI, and simply changing brands can, and will make a difference in POI. Simply changing from one lot number of ammo made by the same manufacturer can make a POI shift. You need to realize that rimfire ammo is not made to the same controlled conditions as centerfire ammo. The only rimfire ammo that is usually repeatable from lot to lot is the premium stuff from places like Eley, RWS, etc.....the expensive target grade ammo. I've been testing rimfire ammo for many years now and I can tell you for a fact that even changing brands of premium target ammo will change the POI in every case. It might not be much with the premium stuff, but it's always there as a change in POI. That being said, I've never, repeat NEVER, seen a 6" POI shift even with the most extreme changes at fifty yards. Even changing from weight, brand, and lot number this would be a gross amount of change. I would expect to see no more than three inches of change of POI at fifty under the most extreme circumstances. What you need to do is get some of everything and see what shoots the best in your gun and try to stock up on that brand and that lot number. My sporter barreled CZ 455 American will shoot right around a half inch for five shots at seventy-five yards with its preferred ammo.
 
What happens is the recoil impulse changes. If you assume the same peak pressure, heavier bullets take longer to get out of the barrel because they aren't traveling as fast, but the recoil force pushing back is determined by pressure, and with this the same magnitude, you expect the muzzle to rise higher by the time a heavier bullet exits. This also means that if you pull on the trigger (common when "ambushing the 10 ring" for a right-handed shooter to pull the gun to the right) or if you don't have the stock recoiling perfectly straight back into your shoulder, or, if there's a bedding problem with the gun, it gives more time for the muzzle to deflect to the right, as well. This compact design with its 18" barrel may simply be light enough that you got some extra spread.

Check that your scope and action screws are tight. Have a friend shoot it to see if he gets the same result.
 
Thanks all i don't know how to answer specific responses but here's the information. The list starts with the lowest and most left amd continues to the highest/right.
CCI A17 17grain V-max bullet (the fastest cartridge)
Hornady brand 17 grain Vmax
CCI TNT 17 grain TNT Hollow points
Hornady XTP 20 grain Hollow points
CCI Game Point 20 grain Hollow points.
The fastest lightest prints the lowest and most left the slowest / heaviest prints highest and right. This would support a recoil management issue. I've had similar experience with spring powered air rifles printing higher with heavier pellets @ close range, BUT nothing this drastic. This rifle has a plastic crap stock that doesn't lend itself to bedding. On top of that it seems to be odd talking about recoil issues in such a light caliber. I'm open to advice on shooting techniques but for the record I've shot sub MOA with several centerfire-rifles and air rifles and they require completely different holds. If there's something I'm doing and can change to make it better I will, but I have shot other 17hmr rifles and they did print a little differently but nothing like this.
Edit
And yes all the scope mounts/rings are tight. Torqued evenly and locktited
21" sporter barrel
 
A rigid stock you can bed would certainly help keep it more consistent. If the stock touches the barrel anywhere (do the dollar bill test where you hold the dollar in a "U" under the barrel and slide it from the muzzle to the action to make sure it doesn't get caught along the way) it may be part of the problem. Even in these little guys, there is barrel bending (slight) and pressure distortion of the barrel than can cause the muzzle to whip. That bending is most likely the cause of the big shift.

Let's try a couple of experiments. The first, assuming you are shooting off the bench, try setting the magazine floor plate on the front bag instead of the front of the stock. See if that mitigates the difference any. Those flimsy stocks, under the weight of the rifle, can actually bend or slump into contact with the barrel which should be avoided, unless...

...you are doing O'Connor bedding. This is where two points on the stock make intentional contact with the barrel that is pre-loaded by 10-20 lbs. Basically, you take a 15 lb. weight and with the gun in a vice or holding onto the buttstock and with the magazine floor plate resting on the front bag, you hang the weight off the front sling swivel. This bends the front stock down. You then insert wood or paper matchstick shims between the forestock and barrel on either side of it until it's jammed tight. Then you remove the weight and try shooting it with 15 lbs of pressure against the barrel at the point where the shims are. You then start over and move the shims back maybe a quarter of an inch and try again. Keep adjusting until you find the sweet spot for your load. Once you do, you take them out one last time, apply the appropriate epoxy or other adhesive and glue the shims in that place. This method will tune the barrel to the load like a barrel tuner, but lighter.
 
I checked the stock and it touches the barrel half way back on the forend. With a significant amount of pressure it appears to lean the left side the hardest because of where the bill gets stuck. The stock has a barrel channel that I could remove for experimental purposes. That would float the barrel but the forend becomes extremely flexible and not to mention ugly without. This a replacement rifle from Savage so on the last one they replaced I ground that channel for clearance to float the barrel but by the time I removed enough material to float the barrel statically the forend was flexing and probably still touching in use. That rifle the ammo disparity was less but was replaced because the first cold shot and only the first cold shot printed 3 MOA randomly low and left from every shot thereafter regardless off ammo used. Not acceptable for a hunting rifle so they replaced it with this one.

Also I'm test shooting off a bench. Left hand holding the forend without touching the barrel and my left forearm steadied by sand bags. Right elbow on the table and the butt consistently tucked into shoulder with light pressure. This is my normal position for testing and zeroing hunting rifles that won't use a bipod in the field. I routinely shoot MOA or better this way with other rifles.
 
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I have successfully glass bedded tupperware stocks in the past and achieved good results in accuracy. Open the barrel channel the length of the stock and glass bed the first six inches under the barrel and up to the tangent point of the radius on the side. If you have the ability to continue beyond this, bed the area around the screws that hold the action to the stock. Just doing the barrel will do wonders for your accuracy...if you're shooting the ammo your gun likes the best. Good luck getting it straightened out.
 
Shot some surplus Indian made .303 and got 8-10" groups. Then I shot some commercial .303 and got 2" groups. Quality matters.
 
I've considered bedding the action forward the front action screw up to the first two or three inches of the barrel. The bedding the rest of the action is too complicated (for me) due to the amount of hollows and undercuts. I've also considered experimenting with a pressure pad under the barrel to dampen the vibrations I guess similar to the O'Connor Bedding. I'm not sure what was meant by upto the tangent of the barrel..
I guess for now I'll remove the offending barrel channel and see if free floating the barrel helps at all. I have a feeling this stock is on its way out, which is a shame because it's light and comfortable.
 
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Sounds like it might be a bedding issue. Start by making sure all the screws are tight.
Roaming groups and group sizes are also why you have to try a box of as many brands of ammo as you can to find the ammo your rifle shoots best.
Indian made .303 is sporadic at the best of times. If it goes bang at all. Mind you, Lee-Enfields do not all have .311" barrel either.
 
My screws are torqued evenly to specs and I've tried all the non Winchester hunting ammo currently available for 17hmr
 
17 HMR seems to be a "one trick pony" shooting one brand, type, shape load better than others and moving POI significantly between ammo choices(sometimes even between lots).
I have 22's that will shoot HV and sub-sonic both open and muffled to the same POI. I have a 17 HMR that shifts POI 8" when the muffler is mounted and different brands of ammo shift 2-3".
 
If removing the channel makes the stock whippy, O'Connor bedding might be the to stop that, assuming you find the right sweet spot. On the other hand, if the channel contact only goes halfway up, then you might be able to supplement the channel with bedding so the contact becomes even on both sides up to that point. You can always whittle it out if it doesn't work. A barrel-diameter sanding drum on a flexible shaft tool works great for that.
 
"The fastest lightest prints the lowest and most left the slowest / heaviest prints highest and right. This would support a recoil management issue. "

This may be an issue. Even with the miniscule recoil of a 17HMR, there is "some movement" if not held uniformly. When I see POI shifts due to ammo change, it's not linear or consistent with bullet weight/velocity.
Any chance you can shoot the rifle from a "lead sled" or similar device to remove the shooter input factor?
 
I don't have a lead sled available for a week and half. I will try the lead sled when I get the chance. I'm wondering if the heavier pressure exerted on the left side barrel by the stock forend is the possibly responsible for the diagonal climb.
 
Free floating barrel had little effects. New problem now

Took this rifle to the range today to test it with the barrel free floated as opposed to the way it was. The disparity between ammo types is the same. Although the groups altogether shifted 1/2" to the right @ 50 yards when free floated.
My new problem is that I dropped the rifle barrel down in the parking lot. Even though it was in a soft case somehow the zipper imprinted on the radius of the crown. I'm already terribly disgusted with this pos but now at myself too for dropping a 1 month old gun. Savage must be making their barrels out of silly putty if a cheap soft case zipper can imprint their steel. I'm considering cutting a couple inches off the barrel to clean up my boo boo and stiffen the barrel. I'm still open for suggestions.
 
rms65,
Don't get upset with this answer, my intentions are good. Get rid of the gun you have and get yourself a CZ 455 in 17hmr. You can even get an extra barrel if you buy it as a combo. I wasn't a CZ fan until two years ago when I finally bought one in .22lr, and eventually got an extra .22mag barrel and a 17hmr barrel. I owned a LOT of Savages over the years and most of them shot well enough, but...they simply weren't in the quality league that CZ is in. Night and day difference in the guns and the CZ's are actually pretty inexpensive considering what you get for your money. My CZ 455 will shoot .22lr rimfire groups well under a half inch at fifty yards with good ammo and it will shoot half inch groups (five shot, not three) at 75 yards with my 17hrm barrel. Either that or get a different stock for your gun and have someone cut the bbl and recrown it for you. It probably will do better than it is now. Good luck.
 
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