Does sandbag resting a pistol affect point of impact?

Hi all, I have a question. I am bench rest testing a Nelson conversion on a 1911 frame. I think I have it sighted in while shooting offhand. But then when I rest it on a sandbag to test fire it, the group moves up to the top of the target frame, in the 5-ring. Is that normal? I know it's not free floated like a national match rifle is, but I wasn't expecting that.

Also, the best group size I got was 3.5" wide at 50 yards with a 10 shot group. The worst group was 4.5". I don't think that is very good accuracy from a sandbag. This is all with iron sights since I don't have a scope or dot. Isn't that poor accuracy?

The offhand vs shooting from rest POI change has been my experience as well. If I shoot from rest it's just to look at group size, not set zero.

I can't figure out if it's something mechanical such as pressure on the lower that is causing it, or if it is because I am looking through the sights differently. I tried doing it while standing, and I had the sandbag on top of my pistol box. Same thing, it hits at or above the 5 ring.

Try resting your arms on the bag instead of the gun. It could be the iron sights too. If you have a combo rail, a cheaper (romeo5, holosun equivalent, ect.) could help the rested group endeavor be a bit more intuitive.

With all that said, if it shoots on call from the hand, I personally would call it good.

Oh, good idea. I'll just rest my arms on it instead of the pistol.

You may go crazy trying to figure this out. Before I got a Ransom, I shot more consistently tighter groups sitting on the ground up against a backstop with elbows on knees.  Groups were tighter than off bags. I still don’t know why; I’m assuming there is something not kept consistent from shot tot shot. Buy or borrow a machine rest. Even here though there is a learning curve FYI.

I'm wondering what would happen if I mounted an old 7x rifle scope I have.


But like you said, I really do need to test this in a ransom rest. I think without that, it's too hard to test. This is a lot harder than testing a rifle.

If you attempt the machine rest, see if you can get some assistance from someone who has some time and experience with one. It takes some time to get consistent with one.

Wow. I thought a machine rest was something that just automatically removed all the variables. I didn't know there was a learning curve.

CO1Mtn wrote:Wow. I thought a machine rest was something that just automatically removed all the variables. I didn't know there was a learning curve.

Learning curve is mostly set up, and the ability to follow the same process between each shot on reset. Think of it like using a lathe or a mill, you can operate one with little assistance and make some good parts, but if you have experience and full understanding of the process you can make excellent parts.

CO1Mtn wrote:Wow. I thought a machine rest was something that just automatically removed all the variables. I didn't know there was a learning curve.

There is a friction mechanism that has to be reset onto a stop for each shot.  Inconsistent resetting will affect the shot.  Additionally, the trigger must be operated identically for every shot, whether using your finger or the rest's trigger system.  A third issue is the tightness of the build. The sights are mounted on the slide, but the rest grips the frame.  Some guns will shoot better via the sights than the rest.

As to bench resting, every pressure on the gun has to be identical from shot to shot.  For sights, I normally use a 1.25-4x crosshair scope.

Sounds funny but try this because it works! 

Put a 5 gallon bucket on the shooting bench then put a range bag on top of that. This should just be very close to how high your arm is while shooting offhand. Rest your hand on the bag and then shoot some groups. If you do this right the zero will not move while shooting a match unless you have a flaw in your shot Routine

For me, when using bags, unless I only let my knuckles/ fingers and the lower portion under the trigger guard come in contact with the bags or rest area, I get poor results. Also, very firm consistent grip. This condition comes closest to actual shooting, or what a RR would hope to do. Give this a try.

It worked, Mr. Allgoodhits. I also used a rifle scope mounted on the top rail. It turns out that the Nelson is capable of much better accuracy than I thought. I simply don't have the talent yet to wield it to its full potential.

OK there are two causes of error when comparing bench to offhand. I) Ballistic Arch many of us shoot with cantted and the ballistic arch and angle change the point of impact. 2) The sight picture is different standing versus a bench. I bench canted until I can confirm a 3 shot one hole group then I adjust until the center of the group is in the x ring standing off hand.

CO1Mtn wrote:It worked, Mr. Allgoodhits. I also used a rifle scope mounted on the top rail. It turns out that the Nelson is capable of much better accuracy than I thought. I simply don't have the talent yet to wield it to its full potential.

Fascinating. Glad I read this thread - thanks x2 to Mr Allgoodhits.

Here are the photos I took. With the scope at 7x, I shot at 25 yards then 50. At 25 yards it was almost one big hole. At 50 yards, group sizes averaged 1.5". I could not eliminate the vibration due to my pulse. I could see the crosshairs vibrating with every heartbeat so I think the pistol would have been even more accurate without that factor.

CCI SV ammo shot the best. Eley bulk was not as good. Federal high velocity WalMart ammo did just as well as Eley but the point of impact was 1" higher at 50 yards, probably because it was high velocity.

I thought this new Nelson kit I got was defective but apparently the problem is not with the equipment. But for some reason the older Nelson kit I bought always shoots better for me. Maybe it is psychological. But I never broke 90 in slow fire with the new kit. And when I first got it, it shot very poorly, around 60 points in slow fire. I have no idea why.

I have read this thread with interest. I have recently sand bag rested a few of my pistols at 50 yards and I did not see my point of impact change much at all vs firing offhand. I did find it a PITA to do on the low bench so I love the 5 gallon bucket technique. I am going to try that next time.

Hey guys please look at the photo of the rimfire cartridge I uploaded. Does that look like a light firing pin strike? That's the best photo my cell phone can take. I've had so many failures to fire recently, about 1 round out of 100. I lost a match due to that so today I installed a stronger mainspring.

I am no expert but it does look light to me. I was getting light firing pin strikes in my Marvel Conversion. Cost me a lot of points in some matches. I switched to a heavier mainspring and have had zero problems since.

Strike looks very light to me

It hardly dents the case at all when I shoot. And that's with a new mainspring too. The gunsmith said it was 20#. I remember my rimfire rifle really puts a dent in the rims of the cases, but not this pistol.

Can you check the firing pin to make sure it is not broken or otherwise damaged? Also how old is the unit and the lower? If all else fails call Marvel. I have found them very helpful.

The lower is a Range Officer that is four years old. The Nelson unit is new. The firing pin does not appear to be damaged. I installed a new mainspring recently, and it's a 20#, although I trimmed 10% off its overall length. If I run it with a full strength mainspring then I get failures to strip from the magazine because the aluminum slide does not have enough inertia to cock the hammer. It's a flaw of the system.

CO1Mtn wrote: I installed a new mainspring recently, and it's a 20#, although I trimmed 10% off its overall length.  of the system.

Aassuming you have a 9 lb recoil spring...go with a stock 20 lb main spring and try an 8 lb recoil spring.

I use a 20 lb main spring and a 9 lb recoil spring in my Marvel and it has never failed to ignite anything i have run through it.

Marvel and nelson use different length recoil springs, nelson being longer.