Touching lands

[bulletdrop]

I have a 308 Winchester bolt action rifle with a Shilen match barrel. I measure the length seated to lands using the Hornady OAL gauge. For most of the bullets I can feel a slight resistance / engagement pretty early in that the bullet clearly engages with something. Then if I apply just a little more pressure on the gauge, the bullet leaps forward quite a bit further.

The difference between what feels like the first engagement and when it is solidly jammed into the lands is as much as 0.150 inches, quite a lot.

Is this a common occurrence? Has anyone else seen this? Does anyone have any idea what might be causing it and if it is cause for any concerns? The rifle shoots well.

 

[Cort]

Do you have a carbon ring built up in the neck area of your chamber? My guess is that you are first encountering the carbon ring that naturally builds up in a chamber just ahead of the end of the neck on your brass and the second engagement point is where your bullet encounters the lands. How many shots have you fired down the barrel and how stringent is your carbon removal process?

Cort

 

[OldManTA]

The other possibility is that the OD of your special case and the ID of the chamber neck are mismatched--the case neck is larger than the neck of the chamber. To make sure that is not the situation push the modified case into the chamber without a bullet installed. If you feel an initial resistance and then it slides forward with some effort the chamber neck may be smaller than SAAMI spec. If the case bottoms out on the shoulder inside the chamber without resistance then there is no neck restriction and the previous writer may have found your problem.
Tom Alves

 

[bulletdrop]

Cort, I have 950 rounds through the barrel. I clean the barrel whenever I shoot the rifle though I do not use a bronze brush (only nylon) so perhaps that is a carbon ring buildup I am feeling. How could I confirm if that is the case, would I need a borescope?

What would be the best way to get rid of a carbon ring?

OldManTA, thanks for that suggestion, I checked the special case without a bullet and it slides all the way in without resistance.

 

[Lapua40X]

...How could I confirm if that is the case, would I need a borescope?

What would be the best way to get rid of a carbon ring?

That's probably the only truly reliable way to determine what's in there.
To rid my chamber of carbon in that area I use a bronze brush (with brass windings) on a rod attached to a rotary tool. The brush is slightly larger than the bullet diamater (.30+ cal for my .284) I use a battery powered screwdriver for its slow turning motor and ease of use in the space available. I first soak the area with solvent (even a simple soaking with Hoppe's works well) then get the brush just deep enough to make good contact with the carbon deposit and turn on the motor. My bore scope tells the final story. Carbon gone............

 

[Cort]

If your eyes are good, you can see the carbon ring with the aid of a bright light. I can see the ring in the chamber of my semi-auto pistols but it takes a bore scope for my rifle chambers.

I would just assume the ring is there and clean the neck area of the chamber. The ring is formed from baked on carbon so you have to be pretty aggressive to remove it. I use a good long soak with hoppes on a patch wrapped around a bronze brush that fits the neck area pretty tightly. I then rotate the bare brush in the neck by hand and repeat the process until the neck area of the chamber is shiny when dried with a clean patch. Many folks use iosso or JB bore paste to scrub the ring out. There is not one fool proof method that is adopted by everyone.

Good luck,

Cort

 

[Drop Port]

Do you stand the rifle upright while measuring? I have seen people set the rifle in a cradle, horizontal and get similar results from gravity, the bottom side of the bullet touching first. I fire a case in my rifle and thread it so tolerance is held to a minimum.

 

[Deleted old_dood]

I have a 308 Winchester bolt action rifle with a Shilen match barrel. I measure the length seated to lands using the Hornady OAL gauge. For most of the bullets I can feel a slight resistance / engagement pretty early in that the bullet clearly engages with something. Then if I apply just a little more pressure on the gauge, the bullet leaps forward quite a bit further.

The difference between what feels like the first engagement and when it is solidly jammed into the lands is as much as 0.150 inches, quite a lot.

Is this a common occurrence? Has anyone else seen this? Does anyone have any idea what might be causing it and if it is cause for any concerns? The rifle shoots well.

I get the exact same thing with my Criterion barrel. I even sent it back to them to have them check the chamber. I received it back and it was the same. They told me there was nothing wrong with the chamber.

 

[Texas Solo]

I too have experienced what you describe. I finally learned to just push through the first bit of resistance to a secondary stop. I then gently tap the rod 3 times and lock it down. Using this method I can get consistent readings +/- .001".
Do it 10 times, then take an average and call it good.

 

[bulletdrop]

Thanks all for the great replies. I am relieved to hear others are having the same experience with no I'll effects. The rifle shoots well so perhaps there is no buildup there but I will be doing the suggested cleaning with oversize brush, hoppes and a slow speed screwdriver.

I will also try drop port's suggestion and do the reading with the rifle upright, I have indeed been doing them horizontally so perhaps gravity comes into play.

 

[Old Navy]

If the bullet sticks in the lead when you remove the tool you are pushing it in to hard or you have the infamous carbon ring. Later! Frank

 

[lpreddick]

i had the same experience and think i found the cause in my situation. i would insert the bullet into the modified case( i had my gunsmith thread a case fired in my chamber). only a small part of the bullet's tip was visible. once chambered i would push the bullet forward and feel a resistance, then release and then stop very slightly into the lands. the early resistance was due to a very slight "crimp" of the mouth of my case. i could duplicate this when pushing the bullet not in the chamber. i ran an expander through the neck and all is well. i would expect a carbon ring to give a continued resistance as the bullet slides over it. also, i suspect a carbon ring won't get thicker than the thickness of the case mouth as it is deposited when the neck is at maximum expansion. the neck contracts .0005 or so after firing and the modified cases are the dimension of a fired case.

 

['Freak]

I get a better, more consistent feel for what’s going on using the Sinclair tool rod held directly against the base of the bullet, not having to deal with shoving through a modified case. The first stop you set indicates base of that bullet with ogive touching and then the second stop is set to the head of any case, preferably one that’s been fully fire formed to that chamber. Add bullet base to ogive dimension to the dimension you get from the tool between the two stops and you have the case head to ogive dimension for seating a dummy round.

 

[jo191145]

The only time I encountered that condition jives with lpreddicks response.
Enlarge the case mouth a thousandths or two and it went away.


You could try inserting the bullet with the modified case backed out of the chamber halfway or with a cleaning rod. Once your past the shoulders with the bullet there should be only one more stop.

 

[bulletdrop]

As an update, I tried measuring with the rifle standing up but no difference. I also did the scrubbing for carbon and I did see some come out but not a whole lot.

playing around with the Hornady tool I did notice that if I fiddle with it some, in certain positions the bullet will go through straight to the lands with no initial resistance. The mouth of the modified case is pretty large so I am thinking the bullet goes in at an angle in certain situations, rubbing against the chamber wall before becoming fully centered and entering the lands.

 

[Patch700]

Seeing as you already have the Hornady comparator for your caliper it would be enlightening to see what numbers you come up with using the stripped bolt method .... I too have the Hornady tool but I no longer use it except for the actual bushing that attaches to the caliper.

When one is talking about being accurate one is saying it's repeatable and for my liking the stripped bolt and a lubed bullet seated long and working back from there is the most repeatable measurement I've ever gotten.

Some imperial wax , a black felt pen , and lots of neck tension used in conjunction with a stripped bolt in a trial and error fashion will in my opinion trump the Hornady tool..

Good luck